Electronic & Hydraulic Shifting (Di2, Ui2, customisations)

I can't work out how to effectively simulate bolt tension in f360

Have you tried applying an area load on the face that's under the bolt head? You probably have to create a feature in the solid model to make that face stand in isolation, although a separate washer body would work and I bet there's a hack possible using Patch to create a zero thickness body to constrain the area over which you apply the load.