Thanks for the reaction, but i don't think you got what i wanted to say.
1. Yes i want to write to the directory when you login with ftp, without doing a change to another dir first.
I managed to do this now with setting the openmediavault variable. (to a share i already had configured on my volume).
The thing i said is that the change didn't happen till i did a fake change in the BUI under the ftp settings.
So setting the variable in the openmediavault file and doing a reboot didn't changed any thing in the proftpd.conf which i guess it should.
So again nothing to do with persistence as i have used the variable OMV_PROFTPD_DEFAULTROOT which makes it persistence.
So the issue i have is you need to trigger the change by changing the ftp settings in the browser admin interface, so i don't know what actually happens when you press the save of ftp settings.
I understand that you need to reload proftpd i did a reboot for that but it didn't pick up the change till i actually changed something in the settings of the web interface.