Will Modifying a Wardrobe Box for Temporary Use/Moving ruin its structural integrity?
I'm not completely sure this is on topic, but I'll try.  I assume you mean one of these:

If you want to cut a hole in it, you'll want to cut it in the "front" and make sure you don't go all the way across it from left to right.  Alternatively, you can just use a boxcutter or utility knife to make the seam deeper for the front flap, so you can just reach in directly.  I know what you mean about the bottom being inaccessible, we had the same issue.