As an alternative to compiling you own build from the source code, if you only want to do things like change values or swap images around you can directly edit the SWF file using programs like
JPEXS Free Flash Decompiler.
While likily not the best way and also quite tedious at times it does work e.g. I don't like Chesire's Bust for Anno[1] and since it is one of only 2 busts for Anno (both of which I don't like) before giving her Huskar Treats which you can't get until Uveto I change it out for Adjatha bust[2] another example is I really don't like the bust change you get after you give Reaha Anusoft so I swapped it back to normal Reaha.
Another Example is I really like both the aesthetic and Flags on the Shock Bow and Premium Armstrong Suit unfortunately both of those items are way weaker than current items which lack what I am looking for, so I change their numbers around to make them competitive with current items.
[1] I think its something about the face that weirds me out, but I can't say specifically what about the face causes this. As a side note I find with Chesire's busts, I either love them like Embry, Aliss, Reaha and most of the others or I feel weirded out by them like the aforementioned Anno, Carl the ever controversial Syri and a few other. While I do dislike other artists bust 99% of the time I can say what about it I don't like it, Chesire is the only one where I can consistantly say "I know I don't like this, but can't point out what about it I don't like".
[2] While you can do this without modifying the game files if I remember correctly it overrides all busts selectable for that character in those circumstances. AKA if you override one of non huskar Anno's clothed busts all of them will look like the override, but naked non huskar Anno and all of huskar Anno's busts will be unaffected.
Side note the worst thing about changing images in this way is every new build the number assigned to each image changes slightly, for example if the bust I wanted to change was number 1426 in this build then next build it might be number 1456. The number doesn't normally change by much normally only about +/- 30 either way but it is frustrating. Also it will change even if no images were added since last build, if I had to guess its likily a result of the compiling.