SPOILER SPOILERS!!!
LOL Yes, you would have absolutely been dunked on. XD Both during midpoint Mercy and end fight Mercy.
And when it comes to variables, there was definitely.... a number. Let's just say... I had to take note of 200+ variables. It was quite the collection. x_x I had a page dedicated to setting the defaults of those variables. If I didn't have that, I think I'd be so lost. Even with the list of variables, I got lost a few times! XD
When Sans says "not to get too close to the edge," he means not to get too close to him that you fall (in romantic/platonic love). That's why the player feels uncomfortable because they feel Sans' being reserved. The main dynamic change for Sans was from reserved to open with his emotions/feelings. <3 (Honestly, I'm a huge Sans simp and I wanted to make a VN so I could fall in love with him. Then I wanted to share that experience with everyone else XD)
In regards to the lines with the SOUL traits, yes. Ren'Py will still see that line as seen, even if the variable within has changed. However, for moments where Sans talks about the expression or the LV, I made sure for each instance to have its own line. This way, if the player was skipping, it wouldn't skip past that. For player experience, it made more sense to stop the player at those blocks of dialogue than to stop the player for one single line with a different SOUL trait.
Thank you so much for all of your questions and for taking the time to comment! And thank you for playing! It really means a lot that you've enjoyed the VN! ;n;