No need to drain the oil to roll in a chain, but there should be an oil change after the new chain is in, to remove any particles that may have fallen in while cutting the old chain.
Don't know about the relief valve, but suspect the oil level would be low enough below the valve point that it wouldn't matter.
'73 280SEL 4.5 (9/72)- RIP
Only 8,173 units built from 5/71 thru 11/72
'02 CLK320 Cabriolet - wifey's mid-life crisis
2012 VW Jetta Sportwagon TDI...at least its a diesel
Non illegitemae carborundum.