I don't think you understand how PHP works
. It's extremely easy to edit you just adjust the css like you would on a non-php site.
Metatags aren't used by any modern search engine and are spam indicators to both Google and Bing(so also Yahoo). They were depreciated years ago. The modern engines calculate keywords from on page content (and will penalize you for spam indicators especially old, old tricks like keyword stuffing, obfuscated keyword text, etc.). SERP means search engine results page aka ranking for a particular search. Metadescription also isn't used in either major engine either as far as inclusion into their SERP algorithms but are used for the results text, so write them to convert users not to influence rank.