I'm asking this before even trying so I won't risk anything in case someone else can tell me already the correct procedure.
I have a mod published, my WIP, dependent only on main and update esm. I want to continue it's developement but including HF as a dependence.
What's the correct procedure to do upload to a new location so the previous one remains published as it is for users who don't have HF?
Thanks

I haven't tested it myself so I can't confirm this but to my knowledge the Workshop differentiates mods only by the Steam user and the mod name. So you should be able to upload your HF version by just renaming the esp to HF.esp and renaming the mod name accordingly, hence leaving the no-HF version as it is.