Now this question is several parts... But beyond the physical process I am more concerned with the question of "should".
First, when labels start to come off is it "wrong" to attempt to re-adhere a label to a cart?
Second, what it the best way to do it, diferent techniques for different carts?

I have noticed that many 3rd party cart manufacturers often use crappy labels that are poorly adhered to cartridges. In particular I have a complete copy of Spiritual Warfare for Genesis (am I the only one who like this game ?) and the label is starting to come off, the rest of it is in good condition and I really believe it to be the result of bad glue. Likewise, my Exodus (genny) also seems to have a bad label. These games aren't exactly common and suffice it to say I would rather repair then replace. Does "fixing" a cart somehow make it less valuable? Is it wrong of me to try?

Now it's one thing to fix (seemingly) poorly constructed carts/labels but what about "fixing" other aestetic blemishes, we have all seen those NES carts that have someone's name (or god knows what else) written on the back. Is there something less complete or perhaps even disingenuine in replacing the back? What do you so called collectors think? Obviously if done one should do so with one as close the original back as possible (rev-a, 5 screw, 3 screw, battery back up specific and what have you) but many NES carts have stamped (or otherwise indented--non printed) numbers and letters, is it "wrong" to replace an NES back with a different stamp?

Whenever I buy a new game I clean it, but where does cleaning end and restoration begin?