Marten, you are a very wise man, not to get into trouble with your family :-) .
I have the same situation as yours, development on my productionn system, but I am able to switch very quickly between 1.7.0 and 1.7.5 on my production system, so this should be workable.
I would very much like to try to adapt vomp to vdr - 1.7.3 + , and I understand your rough sketch competely. I have experience with "scanning through vdr-source-code" to see which functions it provides, so that integration of vdr with its plugins is "optimal".
So if you can provide more details, please do...
PS I have attached a patch with which vompserver plays old PES recordings correctly, also length is ok now, marks are loaded correctly. NOTE THAT NEW TS RECORDINGS WILL NOT PLAY!!!!