While the engine currently supports a P4Changelist argument when launching the editor from the command line, we are only currently using it to check out assets through FPerforceCheckOutWorker::Execute(). At a minimum, we should be applying this and any other globally-specified P4 options to the Delete and Add workers, although ideally we should add them to any P4 command that supports "-c [changelist]":
FPerforceCopyWorker
FPerforceDeleteWorker
FPerforceMarkForAddWorker
FPerforceResolveWorker
FPerforceRevertWorker
1. Launch the editor with the "-P4Changelist" command-line argument
2. Connect to Perforce via the Source Control plugin
3. Add a new asset
Expected Result: The new asset is added to the specified changelist
Observed Result: The new asset is added to a new changelist
There's no existing public thread on this issue, so head over to Questions & Answers just mention UE-36414 in the post.