My reflexes aren't as twitchy as they used to be. Or maybe I just like a little less manic gameplay these days. So a touch slower is a lot more forgiving for me. Some of these jumps feel like flappy bird to me where I just keep dying at the same spot.
Ok, so I launch with
./mame64 c64 -window -flop1 "~/Downloads/Bounty Bob Strikes Back 7HD.d64" -bios jiffydos -joy1 joy -joy2 "" -speed 0.80 -cheat
and with the cheats enabled I can see lots of Overclock CPU entries with u7 = main 6502, u19 = VIC-II, u1 = CIA 1, u2 = CIA 2
and with the -speed 0.80 parameter, mame will honor the speed setting (80% in the upper right speed display).
So how to change this overall speed on the fly? If I underclock the u7 things don't seem to load properly.
I wouldn't mind even typing in a lua command to the console to change the speed factor.