Is it possible to overwrite the fees on a channel when creating a route?

[DerEwige]

Currently I create a PredefinedChannelRoute when doing rebalancing.

I then call sendToRoute with my own PredefinedChannelRoute and Bolt11Invoice.
I tried to follow the code to see where the fees are set for each channel.

For unknown channels it seems to check the Bolt11Invoice for routing hints when creating a FinalizeRoute.

There are two things I try to achieve:

1. Create routes containing private channels (that are known to me including the fees, through 3rd party)
2. Overwrite fees on a given channel (that I know to be different from what eclair believes, for example due to negative inbound fees)

I could achieve 1.) by including routing hints into my Bolt11Invoice.
Would this be somehow possible in a plugin despite this issue: #2802 ?

How would I go about 2.) Can I just create a FinalizeRoute manually and send to it somehow?

A few pointers at the correct sections of code would be helpful.
Thanks