I'm just posting this because I'm very very happy that my UOROM cart worked so well. I got a konami UNROM cart and extend it to use 256KB of ROM, making it an UOROM cart. I also installed a mirroring switch.
Here are some pictures of the mess:

This is my "workbench" after I just finished the board

A close up of the board

The back of it

A close up of some bent pins, so that hayabusafmw knows what they look like

The cart on my NES (there is no way that will fit a game case)

It runs regular 128KB UNROM games

As well as 256KB UOROM games!
I'd like to thank many of you from the NESDEV forums, for explaining me about the mirroring switch, tips on rewiring and all that. Also, big thanks to No Carrier, who helped me obtain the fantastic desoldering iron, that made the task of removing the chips MUCH easier!
I'm now on the process of designing a game to run on this board, and I just hope I'll finish this one! =D