I think you need to do this: if (this.regionId() === 5) {this.erase()};
which you forgot, but while my JS is not the best, I didn't deal with
other plugins modifications, if I don't know what each function will do.
there are parts that I try to learn and understand, which some functions need
to call in another function to work correctly, so I cant help you really on modifify
the plugin in a specific way.
some can edit it like that, if the tileNumber is 2, than it will erase, or if it's 1, but
other plugins might use this function as well, like YEP_SlipperyTiles if not mistaken,
every tile tag with number x are slippery, but regions can also be used.
while tiles can have numbers 0- 7 (0 default), 1-7 are mostly open for things.
if you really want to modify the code, than a coder might be able to help you with it.