It depends upon whether you're on Apache 1.x or 2.x (leading / treatment is different) but the following will work for the "one off" -c- => my-category-c- RewriteRule for either flavor:
The / is required for Apache 1 and assumed by Apache 2 so the optional leading slash ( /? ) will work for both. The QSA flag will append the pre-existing query string and the Last flag terminates that RewriteRule (so it's not automatically ANDed with the next mod_rewrite block).
RewriteRule ^/?-c-([0-9]+)\.html$ index.php?cPath=my-category [QSA,L]
Sorry, I'd thought that the regex in the beginning and code samples would have helped with your aversion to regex.