I would just cw and space it back to correct alignment. I too edit ascii table by hand, and quite often and just find R not very useful in even this case.
In the original vi, if you use cw to change it into a longer word, you can't just use <DEL> to remove spaces after the word, but have to use <ESC> and x. So R is often more practical, and it got into my muscle memory before vim existed.
Or use cw, and then use a plugin like e.g. junegunn/vim-easy-align.