Right now i'm planning to get a Seymour Duncan alnico 2 pro not the slash version for my epi LP. And since there's no metal plating to cover the PUPs is it ok to cover it with a metal plating? Will it affect the tone?
it is said that removing the cover actually make the pups hotter, but i find the change too subtle to be noticed
I'm assuming by "metal plating" you mean "metal cover". It usually cuts a bit of the highs, but the difference should be barely noticeable.
Don't add a metal cover yourself unless you know what you're doing (and I'm fairly sure you don't). It needs to be grounded by soldering to the pickup leads, and will need wax potting to prevent microphonic feedback.