There were some stories published in 1998 by an author who called himself Gangnet, under the umbrella of Permutations (the stories can be found in a number of places on the net, just do a search). The basic gist of the stories is that aliens visit Earth and reverse the characteristics of a brainy, flat-chested girl and a dumb, big-breasted girl. Hilarity ensues as their roles reverse, the girl whose breasts have grown being delighted with the transformation but oblivious to her diminished IQ. The story takes a number of interesting and unexpected turns, with lots of transformations.
This is the introductory transformation:
In moments, a hole in the wall opened up like magic and a bunch of new little aliens, all exactly the same, came running in. They stared at the two girls with total intrigue and then began chattering away all at once. Lizzie couldn’t focus on any one of them and missed it all, like crowd noise. Obviously they didn’t have that problem. Finally, two or three of them went to the controls and began turning gooey-looking dials as the others all stood watching. A brighter light switched on right above Lizzie’s head, like a spotlight. She saw one go on over Samantha at the same moment. And then they pushed some more controls and a loud humming noise filled the room.
The aliens stared at them with rapt attention, except for one at the controls who kept adjusting dials furiously. What was happening? Obviously something was supposed to happen. Lizzie didn’t understand at first what was so damn interesting. Mebbie they were just kind of scanning her. No, most were more interested in her and Samantha than any readouts. Lizzie still didn’t get it, but it was a little easier to move. This stuff wasn’t so tight on her. It wasn’t pinching her hips as much and didn’t hurt her boobs anymore. They were releasing it. At least the little pricks were trying to make her comfortable. Only by the way Sammie was struggling, it seemed to be having the opposite effect on her. She gave out muffled moans like the plastic was getting tighter. Lizzie saw it actually tighten a bit on her in places. As it tightened, Lizzie remarked to herself that with those dowdy clothes off, Sammie’s figure was actually a little better than they gave her credit for. She wasn’t half the stick-insect she’d looked like. Her long skirts did nothing to show off those hips. As for her chest, it wasn’t really that bad after all. Lizzie still wasn’t getting it until she heard the word “Faster!” in her mind, and the alien at the controls jiggled the dials. Then she could actually see the effect before her eyes. Sammie’s boobs blew up to fabulous proportions. Why they were almost as good as -
Lizzie let out a muffled shriek and struggled like crazy. No, no! They couldn’t do this! Her own tits were deflating as Sammie’s got bigger! These fucking aliens were giving her Lizzie’s boobs! “No! No! Stop it!” she wanted to scream. “You can’t do this!” Somehow the aliens heard her… but they ignored her. And made a noise that sounded like chuckling.
The cellophane was growing tighter again, even as Samantha began to relax a bit. It was hard to get a good look, but Lizzie’s heart fell as it sunk in what’d happened. Samantha was stacked now. Her boobs were every bit as good as Lizzie’s had been… and her own chest looked like a flatland. This wasn’t fair. It really wasn’t. Lizzie just tried to close her eyes, but she couldn’t even do that, the cellophane was so tight on her face. She just wanted this hideous experiment over, and her boobs back. They were gonna put it all back, right? Lizzie would have heard about stories like this. They were just fucking around, but it’d all be all right in the end. The aliens weren’t even looking at her anymore, only Samantha. And then the smell of the stuff coming into her nostrils became kinda funny, and she blacked out.
Lizzie came to on the road not far from Samantha’s house. She was back in her cheerleader outfit, and her math book and purse were lying in the grass not far away. She’d just blacked out on the way to Sammie’s house. Of course. She thrust her hands to her chest and screamed. “Oh, God, no! This can’t be happening!”
She ran all the way home and up to her room, stripping down to her bra and undies and looking into her full length mirror. The bra was useless. The fucking gray little bastards had a sense of humor by putting it back on her at all. Her hips didn’t look as good as they had either. “Oh, God, no…” she sobbed. “No, anything but that…” Why couldn’t they have struck her deaf? Even blind! Anything but her boobs! She began hyperventilating and finally passed out again.
And here’s one from several chapters in, as one of the girls uses her enhanced IQ to apply the technology to other women:
Apparently the redhead was drawing on all six of the other girls, for at first kim didn’t notice any definite change in them as her own chest began to fill out again. but slowly their chests began to deflate. none of them looked too happy about it, but one girl seemed, behind that sound-proof barrier, to be going into hysterics. apparently she’d been here for a few days at least but hadn’t known about anything like this. kim couldn’t help feeling a little better in spite of herself as her breasts slowly returned to their natural size, but she hated herself for it. if only there were a mirror… no, god, what was she talking about? this was all insane! she kept turning her attention from her own growing mammaries to the deflating chests of the other girls and back again. it went much slower with them than with her, apparently because it was six to one and she was taking boobs from all of them. taking boobs! it sounded ridiculous. the sadistic, now-stacked redhead who was putting them through all of this might have all sorts of technical terms for it, but really that was what it amounted to. she was getting their breasts. “my god, that’s enough!” she shrieked, looking back to her own chest. she thrust her hands around her ballooning pair as if to hold them in place, but her fingers just kept slipping as she found herself holding less and less, until finally her palms were covering little more than than her nipples themselves. “for the love of god, stop!” she screamed. her boobs were now the size of basketballs and still growing. the other girls were still deflating, but none of them had much left. “no, please! i’m grotesque! it’s too much!”
This is a foundational breast expansion story and it’s one I return to every few years to enjoy anew.