301 Redirect Question Related to Backlinks

I wanted to place a keyword in my URL (not exact match but at least semi) so it helps with rankings for specific keywords (I'm seeing plenty of EMDs ranking very well).

I read in passing that if you do a redirect, your links which point to the old domain still give credit to your new domain name, but that only a certain % of the juice is passed along.

Should I bother to have all links pointing to the old domain changed to the new one? Or just simply build all new incoming links to the new redirected domain?

Thanks

I would redirect the site then i would work on building new links as well.

Redirect the site first and then do the other

Certain % of link juice, that thing doesn't apply anymore.