You can also accomplish that with any global search/replace programm that has the ability to recognize and work with multiple file extensions (such as .doc .tpl .php .css .html and so on) and subfolders at the same time. The only problem with what was said above, appears when modified templates share the same colors for text, textlinks and background ... where you might want changes between those too. But in that case you can always look for the specific .tpl file and then insert your own code changes right there, causing that to effectively by-pass the css files and/or the search/replace changes that had been made.
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