Adding PL languages laster

Hello,

I'm definitely a novice, I installed postgresql about 2 weeks ago, and
now several people are testing databases on it.  I tried moving some
functions in and realized I had to add a language to be able to create
functions, I was easily able to install and use the plpgsql language. 
Now I'd like to add either perl or python, I see instructions to do it
when installing postgresql, but, can I add it now that the product is
built and running???


Thanks in advance,
John