This is the most incredible video I’ve been looking for exactly this for a couple days. Going through tons of trial and error with 3d printing threads.
There are almost always multiple ways to do something in SOLIDWORKS. Combine is probably the more commonly used feature to accomplish this, but an indent would work too. Good idea!
You can apply the scale feature to individual bodies in the command manager. I would suggest using the Split feature to cut the bolt into 2 bodies so that you can scale only the threaded feature and leave the head of the bolt as-is.