Just for the record (this could very well be a NOT recommended procedure), I was able to fix an A1200 keyboard flat cable that I had accidentally damaged by peeling off ~1.5 cm of the green cover layer.
Since the normally exposed part was already partly destroyed (again, my fault) I decided to cut it off completely, then the remaining part - after the peeling treatment - just slid into the keyboard connector on the motherboard and everything started working again flawlessly.
I have no idea how much this is going to last, but considering this A1200 restoration is now complete I hope fiddling with the flat cable as little as possible *might* prove effective.
Feel free to tell me whether I did an utterly stupid thing or not by the way.
(it's not like I had so many options available to be honest... it was either this, or keeping a non-working keyboard, so I said to myself "ok, there's probably nothing to lose")