Hi, can you try just calling StopJumping when player is starting wallrun? I haven’t tested it myself, but as I can see the Character.cpp code, StopJumping calls ResetJumpState which sets JumpCurrentCount to 0, so hopefully it will do the job.
Regarding your question about changing cpp code, usually something is only readable for a reason. And even if it’s fine to adjust, still to make this change work you would need to download UE source, modify it there and recompile everything. Quite problematic just to change one variable.