My application has potentially a huge number of arguments passed in and I want to avoid the memory of hit duplicating the arguments into a filtered list. I would like to filter them in place but I am pretty sure that messing with argv array itself, or any of the data it points to, is probably not advisable. Any suggestions?
Once argv has been passed into the main method, you can treat it like any other C array - change it in place as you like, just be aware of what you're doing with it. The contents of the array don't have an effect on the return code or execution of the program other than what you explicitly do with it in code. I can't think of any reason it wouldn't "be advisable" to treat it specially.
Of course, you still need to take care about accidentally accessing memory beyond the bounds of argv. The flip side of it being accessible like a normal C array is that it's also prone to access errors just like any other normal C array. (Thanks to all who pointed this out in comments and other responses!)