I have the following simple line:
inoremap <silent> <TAB> <C-o>:set foldmethod=manual<cr>
However, after this command is run and I run set foldmethod?, it reports the foldmethod is still set to syntax.
To be sure this map is getting triggered, I added
<C-o>:set fdm=manual <bar> :let blah = 222<cr> to the map and
echo blah reports 222 as expected.