You certainly should not be modifying the # BEGIN WordPress block, as this is likely to be overridden by WordPress itself.
You should create a new section before the WordPress front-controller. This will work just as well and keep the directives separate.
There is no need to use a <IfModule mod_rewrite.c> wrapper, in fact you should not use a wrapper in this instance, since your plugin would seem to be dependent on mod_rewrite being enabled. Your plugin will not function correctly if mod_rewrite is not available, so you shouldn’t “fail silently” if it isn’t.
Aside: There is also no need to repeat the RewriteEngine and RewriteBase directives. If you are hand-coding the .htaccess file then you would not duplicate them. However, if you are injecting this code programmatically, then you probably need to – to be sure. (Multiple RewriteEngine and RewriteBase directives are not strictly supported. The last instance in any given context wins and controls the entire file. For example, if you place RewriteEngine Off as the very last directive in the .htaccess file then it is Off for the entire file, despite there being earlier RewriteEngine On directives.)