I wanted to ask, if it would be possible change Sera's color back to her original color even though I have already finished her acquisition quest
AFAIK, using a save editor to change Sera's values would be the only option besides reloading before the acquisition quest.
Someone here may be to tell you the values to change but I haven't messed around with editing values, flags, or anything really besides stats, money, items, and appearance, so I'm not much help there.
Is their a way I can have a super large dick but still be able to fuck any hole? What exactly determines this like length or thickness or both? And is their a way to go into the save editor to make it so it won't matter?
I may be misremembering if it was a feature in CoC1/2, but I do believe there's either a cheat or an option to essentially ignore size requirements. But again, that may be my brain just rotted from CoC2, but as someone else commented, Condensol will temporarily shrink your size by, I believe, half. Condensol can be purchased from Sera on Tavros (if you've bought her, you must encourage her to continue her attempts at business to regain access to her shop) or Gene, the big red bat thing, on Myrellion.
To answer the first part, at least the best I can, there's a stat called 'capacity', which is a combination of length and thickness, for each character that you can have sex with. Some NPCs may also have hard limits to restrict sex, as an example the bunny girl on Uveto has a hard lock on sex for anything at 12' or larger.
Your best option is just use the infinite item use cheat, keep a Condensol in your inventory, and pop it when you need to shrink down your tree trunk to a branch.
I'm actually kind of shocked that there are people still coming into this and CoC's thread asking when the game will be "finished", as if Fen, Savin, and Co. haven't been using TiTs & CoC2 as their own personal fetish dump that they occasionally throw a halfway-decently written character in incomplete and promise updates(which if they are ever updated, it's an update to give them a dick or someone on the team inserting their own fetish) so that they can continue raking in ten's of thousands every month from the degenerates throwing away their 'tism bucks.
I gave up on TiTs a long time ago and I basically just check in on CoC2 every so often to see how many more dickgirls, 'cuckold'/voyeur scenes, and removal/backsliding on the Corruption aspects of certain characters.
At this point, I think the only thing that could bother me is if Byvernia in CoC2 got an update that involved turning her into a dickgirl or hooking her up with another Taeleer, like Quinn.
Shit, I better shut up. It's a known fact that they read these threads and I don't want to give them any ideas. Especially with Savin who's admitted to writing content purely to piss off players.