Dan,
To add to my earlier answer in the thread in the Quantum Mechanic forum:
1) Type is NOT the filename suffix, just an indicator of the file type (e.g. NNEF, CCR2, TIFF, JPEG, etc.)
2) Your use of the {type} variable in the renaming template does this. You do not want to include it; the filename suffix (e.g. .tif, .jpg, .cr2, etc.) is ALWAYS added by PhotoMechanic (you can not even get rid of it, only tell PM to make it upper or lower case, via the preferences). Just change your renaming string to img_{dats}-{tims} and you'll be fine.
3) This is not possible in the way you want it. But if you start the file renaming (keyboard shortcut: CMD/CTRL-M) you can edit the renaming template. If you want to edit the file names on a per file basis, you can do that in the contact sheet by double clicking on the filename underneath the thumbnail.
Hope this clarifies things a bit more,
Hayo