No. Evars weren't designed to be dynamic. I don't know if indiestep's !setvar ever worked/works. (it didn't for me when I tried only once a while back with an anonymous build).

Since I separate mzscript scripts from the step.rc (there's an option to use the step), I just include my varfiles which have variables specifically named as module settings, so that they become evars. The version of mzscript I use does not support spaces/quotes in variables' values, so I use textedit2 for those. Then to apply changes I !reload and !reloadmodule versus a slower and excessive !recycle . The only elegance is in the final experience (if all goes well).