Programmatically change the datasource of a join (IRelQuery DestinationTable ??)

Hello everybody

I'm trying to change the datasource of a join.
The reason for that is the following: I read the source out of an given Lyr-File, in which the path is abolute. If I load another project, I want the datasource to be the one I load, and not the one standing in the lyr. That's why I need to change that. (This Lyr thing is not important for the question but it may give you a better understanding. Otherwise the lyr can be seen as a static file which contains sources and tablenames).

For illustration:
This is the source I load. (Q:datasource\ele1_testings_fgdb\...
Attachment 34678

This is the source standing in the lyr and used for the join. (Q:\datasources\ele1_testing_mdb\...
Attachment 34679

So how it's done?

Thanks for every hint!

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