Update: Web2Manager 0.3.3
I found creating a Manager user from a Web user a more common task (at least for me), thus I added the functionality to this plugin. (ZIP file attached)
Recommendation
Tbh I originally disliked the fact that Manager and Web users are separated however, prefer it this way now. Thanks to this plugin, but also because I found it useful to have a clean overview of who is able to access the Manager.

I recommend to let everyone sign up as web user then promote the ’managers’ using this plugin.
Changes
- Added a Web->Manager functionality. It finally lives up to its name now.

- Checkbox on Web user profiles is disabled by default (to safe admins from accidentally promoting members to Manager users).
- Fixed a few other issues and compatibility restrictions (e.g. editing didn’t work for me before, fixed now).
- Added a ReadMe file with description and installation guide
Test & Version
I made this on MODx Evolution 1.0.2 and tested all options and combinations systematically. If you face problems getting it to run, please add more infos than a "this doesn’t work for me" kind of reply. Any other feedback is appreciated as well.
@Staff
You can replace the old version in the repository with this one (if you want), since it still shows the very first version which doesn’t even work on the current MODx release.
And...
Have FUN!