Can you only encounter the "Liberation day" character Riley once per year? Wiki kind of suggests you can meet her multiple times, just with the initial meeting only happening once. So far though, I've only been able to meet her once a few days ago, and she hasn't shown up since.
If Silly Mode is turned off, yes. If it's turned on, she always has a 0.5% chance of appearing regardless of if you've met her this year or if it's near July 4th. I actually find it a bit annoying, since you always have to pick which variant of her you'll get before you can leave.
semi-related: Is there any good way to reduce willpower without risking transformation (horse pill) or loss of other stats (dumbfuck)?
Save editing. As for in-game only methods, not really. The non-TF way with the fewest side effects is also the one with the most hassle to get it: you'll need to try opening the red-keyholed door in Po's Ship with an unsuitable cock type (i.e. not canine, no knot, and colour isn't red, crimson or scarlet) and max Taint. It's randomly selected from up to three scenes:
- The basic scene, which has no requirements but varies with your Taint, and the 'at least 100 Taint' variant is the one with the stat losses;
- Getting an 8-hour version of priapism whose timer doesn't decrease with each orgasm, which requires not already having priapism; and
- Growing the selected cock by a small amount, which requires the selected cock be less than 16" (with the Mini perk), 30" (with the Hung perk) or 20" (with neither).
So to maximise the chance of getting the scene you want, you'll need priapism and for the selected cock to be sufficiently large. Even then, that scene can only reduce Willpower by 1, and it has a 50% chance to reduce Intelligence by 1 instead so long as both are >1, so unless you only have 1 Intelligence you'll still have to do some save-scumming. It also takes ~5 hours each time, so using this to lose all your Willpower is likely going to result in Kiro being fully bimbofied.
If you can't do that or don't want to, the next 'best' way has many more side effects but is much less of a hassle to use; after uplifting the pexiga, and so long as Doctor Badger hasn't been arrested, use a big dose of the Dollmaker's Brainmelt Lamp, which will reduce Willpower by 20 and Intelligence by 5, increase Libido by 15 and Taint by 2, and grant the Weak Mind perk if you don't already have it.