I ended up fixing the thing with the hairpin lace by unraveling loops till I came to a point where I could put them back on the loom without the loom popping apart. Wheee, tension. ;D But I didn't feel like working on it after that, so I picked up Brian's much-abused pirate/fighting shirt and set to mending the re-tear and, so as to avoid a re-re-tear, finally putting in those gussets. I like gussets. ;)
As of right now I have one gusset set in, and I'm about to tear out the armpit of the other side so I can put in the second one. It must get done tonight, since Brian can't very well fight with a shirt with a giant hole in the armpit. ;D
Next shirt modifications: Actually put a patch behind the mend (I know, I should have done it before, but I figured the gusset would help keep it from happening again more than the patch ;)), and put drawstring casings on the sleeves. After that, when I have time, I ought to actually just put cuffs on, but that's probably not happening in the next couple of weeks, and the casing is a quicker, workable fix.