Market Press excerpt function

I have been trying to edit the function (product_excerpt():wink: so that i have have longer descriptions when i do a category listing. My changes don't seem to be showing on the site. Am i wrong in thinking that the excerpt it being generated dynamically each time, or are you saving the values to the DB?

I have changed line 2466 so it reads: $excerpt_length = apply_filters('excerpt_length', 350);

Many thanks,

Andy

PS: could you also tell me what the $mp variable is for.