if you're able to write a scheduled task to run a sql script to update the database you could do it.
SET KeyValue = CONVERT(varchar(36),newid())
WHERE KeyName = 'SkinVersion'
However site settings is cached for a few minutes at a time by default so the change would not happen instantly if the cache was new.
Also seems a very weird thing to ever need to do this, skins don't normally change that frequently.