In the file "HackGame.tap" there is a patch for JR that starts at address 24039.

Save a "Bytes" header of address 24064 and of 8503 in length, if the datablock
gets saved along then just delete it from the save file in post or just load
the header from it. Then load the main headerless block but before you load just
remember to do a CLEAR 24038. After the load do a RANDOMIZE USR 24083 to decrypt
the game.

Then load in the patch and save it with SAVE "GAME"CODE 24039,8528
and before you load it back in remember to do a CLEAR 24038. To start
it use RANDOMIZE USR 24042.

If you want a new loader for the hack then that is provided with the game
"Guess the number". All you have to do is to assemble the file JRMLodx.asm
with a new RAMTOP address and load in the file JRMLodx.tap and resave it
with the header screen or SAVE "SCREEN"CODE 24042,555.

Then to build a single game file you do:
copy /b jrlxxx.tap+jrmlodx.tap+[your game file] JET-ROCKET-HACK.TAP

The POKE for infinite lives is POKE 27924,0.

That's it.