The only way I can use my preferred weapons loadouts was to use FMB and edit missions to use my custom set. I tried overwriting the default set and naming my preferred loadout default but it didn't work for me. I will look at that again as that method would save a lot of hassle.

EDIT:

No need to use FMB, you can copy paste your saved weapons loadouts into any of the stock misssions using notepad - this works and straightforward to do.

Overwriting Default does not work.......I set up the Spit with Tracers, saved as default, deleted all other profiles, into a mission - no tracers.