Question

I want to assign different commands depending on context.

I’m trying to do something like this:

if line is empty:
    map x key to y command
else
    map x key to z command

Answer 1

It is normally achieved by <expr> mapping:

nnoremap <expr> ((empty(getline('.')))?('y'):('z'))

As you are going to use NerdCommenter, you are forced not to use “nore”:

nmap <expr> empty(getline('.')) ? '' : '\cc'

Replace '' with the desired code as I do not understand what you mean by “appending a comment”.