"If you're so interested in the lower half, why not go for it?" Geoff proposed. "And I guess some floppy ears would just be stylistic. I'm still thinking two legs is fun though, so why don't you be a donkeytaur and I'll be a donkey satyr?"
"Go for it." Jeff said. "Set the duration for a few days, and we can extend it to indefinite later if we're good with it or cancel early."
Strategically copying over some donkey data from the backups, Geoff customized his lower half and let the Chronivac do the auto-fill on Jeff, giving them both long ears and making some subtle modifications to facial structure, and...confirmed. Set reality compliance to get some similarly hybridized family, and...
Geoff let his pants drop (they were optional), revealing an oversized tool with which he was familiar but hadn't had the limbs to examine in detail before, and some hind limbs he'd felt familiar with in overall structure but not in angle and orientation. He flopped up a bit and stepped away from the chair, kicking a bit experimentally. On the other side of the room, Jeff's lower body seemed to double its legs and stretch backward, growing shaggy gray fur as the feet condensed into hooves. He whipped around his tail a bit and raised individual legs, getting used to the quadrupedal lower half with a lot more upper-body control (including a suspiciously flexible joint where donkey shoulders segued into human torso, flopping all the way forward and back up again).
And a matchingly large tool, the sight of which aroused Geoff all over again. Homosexual donkey, yo.
"Dude." he said. "We could totally try that penetration fantasy you had like, now. I'll enable some cleansing data and stretching on both of us if you want."
"Hell yes." Jeff said, patting himself on the withers. "Do it, and do me."
A few Chronivac edits later, Geoff lined up his massive anatomy and mounted Jeff, humping indiscreetly and braying proud. The two of them continued like this for a while, Jeff's front half throwing off his shirt and playing with his nipples out of not much else to do. Awkwardly managing to reach around and jerk his counterpart, Geoff drove Jeff to orgasm first before leaving a massive creampie in his brother's ass (and avoided getting swat by the tail afterward). One of the cleaning edits he'd made was that their cum would clean up messes instead of make them, clearing away dirt and sorting objects back into place before dissipating and taking the smell with them. And of course, everyone would be okay about the very public indecency they'd commit in the process of this 'cleaning'.
Pulling out and clambering atop his sibling, Geoff hauled himself forward and managed to get beside Jeff's head in order to give him some aftermath kisses, softening cock still leaking excess cum on Jeff's back as ears were gently scratched.
Geoff pulled back from kissing and said "Alright, we're totally taking this machine with us, just reconfigure our comp into a laptop or something. I've got some ideas. We'll see how this transformation affects life for a bit and see what comes next."
Jeff's ears swiveled forward at that.