Relabel 'time_stamp' to 'timeStamp' in pump

Tyk pump uses “time_stamp” as label in with prometheus integration here

but I need to replace it with timeStamp. Is there a way to do this within pump’s config?

No, this is not possible via the config. The time_stamp field is hardcoded into the pump’s source. You could change the value in the source and build a custom version of pump.