Covering up a hoop can be done with many things, but essentially, this idea is about cutting up a medium, lets say aluminun foil, to fit the hoop. Then cut out the center for spraying. It can be a lot of work and reuse of the cover up is limited.
Sticky hoops are relative to what caused the stickiness to begin with. If you know that, you may be able to check the label to determine the removal process.
Rubbing alcohol can remove a lot of glues. Test a small area of your frame because damage is expensive!!!
I have pretty much given up on using adhesives. There are a few reasons, one of which is seen in this photo:

I sprayed the stabilizer with adhesive but missed an area and the fabric was free to move - and DID.
I use (almost exclusely) the AnnTheGran adhesive stabilizers. This one is a medium weight and if I need more stabilizer, I use a simple tearaway under thewhole project.
Adhesive on your hoop will make for a bad project possibly leaving a mark on it. Sprays can be subject to age, humidity and amount of spray (something like I am). Do I use them? Very rarely, but I do.
If you are interested in selling your projects, you can determine your costs and profits quickly with my Spreadsheet.
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If you want to see my pashminas (that I successfully sell retail) check them out here. I also wholesale them.