Before editing it would be a good idea to make a copy of the original .htaccess file in case something goes wrong…..
The single line(s) can go on their own individual lines. At the end of the file should be fine, just don’t break up connected sets of lines like the permalinks settings.
301 is a ‘Permanently Moved’ redirect (there are others include temp redirect) – google (and others) crawling your site should know what it means…..
Unless you have problems with the htaccess file, there is no reason to remove the lines from htaccess, so anybody who comes across them in future should also be seamlessly redirected…
It can take a surprisingly long time until google is fully updated.