I have successfully removed pads before and re-used them on other tanks. But like DollysMom stated it requires a great deal of patience and care. Those pads have very thin coils of wire running through them and if you stretch one or break it, the pad will probably be useless.
I used a hard flat plastic spatula like you might have in the kitchen, and some Fingernail Polish remover. Gently work the spatula under a corner of the pad, use a Q-Tip and rub some Polish Remover under it, (The Fingernail Polish Remover will dissolve the glue). And just keep working it. It will take a few minutes but I was able to remove one from an old tank like this.
Of course after that, you will not be able to stick it back on as intended. But again, like DollysMom stated, most of us today don't stick them directly to the glass anyway. Get some of that industrial grade HVAC Foil tape and tape the pad to a piece of aluminum foil. Then tape that foil to the cage bottom. Later if you want to remove it, you just cut the foil tape loose.
You can find this foil tape at most hardware stores, or even in the tool section at Walmart.