What a joy it was to depot over 40 different palettes and compacts into just 7! I really mean that; I found the practice almost meditative.

After trying many different methods, this is what works best:

Soak the edges of the pan with high percentage rubbing alcohol (don’t worry about ruining the makeup; the texture of the product won’t be different once it’s dry again)
Wait 20-30 seconds for the glue to soften
Use a slender, sharp tool to dig between the metal makeup pan and the plastic compact; make sure that you have really wiggled your tool UNDER the pan rather than just piercing its side
If the makeup cracks or shatters, soak the pan with the alcohol, press the makeup down firmly with a paper towel to repress it, and keep working on its removal. you can do this as many times as necessary
Lift the pan out of the compact and clean excess glue off the bottom with the alcohol. i find it helps to flip the pan over, spray a little alcohol on, wait 30 seconds, and rub off as much as possible with a paper towel. i repeat as many times as necessary and will scrape off stubborn glue with my fingernail
If the pan had to be repressed, leave it out to air dry overnight
If the makeup is dry, test to see if the pan sticks to your empty magnetic palette. if it does, great! if not, put a magnetic sticker on the back of the pan, place in your palette and voila!

The Supplies I Highly Recommend (and I tried a few different duds that are not mentioned here):

Empty Magnetic Palettes from Shop Miss A: These are the cheapest palettes I could find that are still both attractive and effective. I like organizing my makeup by using one print per product type; so, for example, all my blushes from now on will go in multiples of the black palm print palette, while all bronzers will go in the faux wood print palettes
Rubbing Alcohol: I like 91% because the goal is to find a balance between having as little water as possible (water is what ruins makeup textures, not alcohol) and not having it dry up too fast. Rubbing alcohol typically comes in 70%, 91% and 99%+ concentrations, and I prefer 91%. Also, don’t underestimate the amount of alcohol needed for the job! To do this project I used about 5 oz.
Spray Bottle: I find smaller (8-12 oz), lightweight plastic bottles the easiest to handle, but to each their own, The most important thing is that it shoots more of a stream, not a fine mist
Paper Towels or Napkins: Toilet paper, facial cotton or similar are too soft and will leave filaments in repressed product
Depotting utensil: It’s not necessary to buy specialized tools if you have something that works (like my jacked up dollar store scissor!) but they’re undeniably better at the job. Similarly, one spatula will do and once you’ve practiced, you will get better and better at not damaging pans. But if you want every pan to come out as perfectly as possible, different shapes of spatula can’t hurt.
Magnetic stickers: Buy more than you think you need, and make sure to get two sizes: the standard 1 inch rounds but also the half inch rectangles. Too big stickers on tiny pans are a waste of space in your space-saving palette!