Yes, most Basics had peek and poke commands with which you could read and write specific memory locations. For example - parentheses may or may net be needed, depending on the Basic implementation:
X = PEEK( 123 )
would read the byte at memory location 123 and store its value in X. Then
POKE( 123, 42 )
would change the byte at 123 to be 42.
But these didn't normally have so much to do with patching executables to add/change functionality.
That unlocked a memory of me seeing my computer lab teacher after class in 5th or 6th grade to ask her about the applications of PEEK and POKE. I’d picked up a copy of the GW-BASIC manual from a used bookstore. She’d never heard of those commands. Ended up promptly locking up one of the school computers by poking random numbers to random addresses.
I remember looking into BASIC sources to figure out how they did some things I had no idea how to do with BASIC... and finding POKE statements with weird numbers, it was looking a bit like magic... (I was probably 10 or so, though)
But these didn't normally have so much to do with patching executables to add/change functionality.