The typical suggestion seems to be to use something like Dropbox or Github to sync the files between a mod team, although if the uploader of a mod retires the entire mod has to be reuploaded by an active member of the team. A quick google turns up people asking the same question and getting a negative answer, but even those threads seem to be at least a year old.

Hopefully I’m not spreading misinformation here, as I’ll admit it has been years since I was a mod author using the Steam workshop. It’s potentially a limitation to collaborative efforts, but AFAIK there’s no way to approve a second mod author and give them editing privileges on the Steam workshop. Vista Oil & Gas Hazard Identification (HAZID) Studies Terms of Reference (TOR) 01 June 2019 1 INTRODUCTION Hazard Identification (HAZID) is a brainstorming workshop with a multi-disciplinary team to identify potential hazards. I mostly keep up with the Workshop as a user, and IIRC I have never seen more than one listed mod author account on Workshop files. As far as I am aware, Steam workshop is done on a per-account basis, so far as I know when I dealt with it for a Dungeons of Dredmor mod I made for myself and uploaded in case others wanted the same functionality.

Steam workshop terms of service