I don't know what the clip's like on the FOP38, but it should come off without too much fuss (I had a taisol with a crap clip and I had to use pliers and a lot of force to get it on, probably lucky not to kill my core). The thermal paste should just be between the raised cpu core and the hsf - the L1 bridges are on the ceramic away from the core, so they won't be affected by thermal paste. If it's thermal paste like arctic silver it'll just wipe off - anything like a thermal pad will have to be scraped off, use something that won't sratch the cpu or heatsink like a plastic knife or toothpick.