This may be the first reference to either of these subroutines (that I'm aware of) in nearly 25 years! Perhaps Karli (or Larry Frick) was the motivation behind their creation? (Most of the undocumented subroutines are ones that we converted from assembler for a particular developer, who wouldn't benefit from us documenting what they had presumably designed.) Fortunately, the code is quite simple for both of these, which act like simplified versions of COMMON, using the fixed packet name "PEPOKE". .
To answer your first question, the PEEK routine does pre-clear the argument you pass, regardless of its size. In fact, there is no specific size for the parameter to either routine. Since it is just a front-end to the common/shared XCALL COMMON core function, the size depends on the MIAME.INI directive
SBR=MSGSIZ.
If your MSGSIZ=512, POKE will only store the first 512 bytes of the packet you pass, and that would be the maximum that PEEK can possibly read. But there's nothing stopping you from setting MSGSIZ to 513 or 15987. In any case, the MSGSIZ specification only sets the
maximum size that can be stored; you can always store and retrieve smaller packets. So yes, your plan is safe.
