Hi,
I never liked custom thumbnails before, because I keep my CC at minimum and I didn't see any need for them. But recently I started to create contacts (as face masks) and it's really difficult to see them in CAS, the whole Sim face as a thumbnail isn't very nice so I've tried making a custom one. I followed Tamo's tutorial for this, but it helped only on my lipsticks but not on face masks. I know that there's one tutorial for this here on MTS, but it seems to work only on CC created with CTU. I make my contacts with Workshop (I've tried to remake them with CTU, but they didn't work), so if anyone can help me, I will be grateful

Unfortunately, I've broken my copy of CTU during testing of new features, and can no longer get to any costume makeup, so, ahem, these are the long instructions...

Note down the Instance of your makeup. I'm not sure if TSRW displays instances ordinarily; if not, open the file in S3PE and just copy the Instance from the CASP.
Go to Docs/The Sims 3/Thumbnails and open CASThumbnails.package in S3PE, then use the filters to filter for your Instance number. Note that you do have to have used the makeup ingame for this - but I'm sure you have. There should be one THUM resource left after filtering; extract it as a PNG (don't rename it, since you'll need to reimport it using the same Type/Group/Instance, and the easiest way to do this is to just let S3PE grab that information automatically from the filename), edit it, and then import it into your .package file and delete CASThumbnails.package (it'll regenerate).

Thank you for this priceless information
I'm stuck with the step when I need to import edited thumbnail back, so I should chose Replace or Add? Because neither way it worked so far. And when importing do I need to change something?
I'm having a feeling that my PC has to do something with that, it's so full of crap