I couple of years ago I cut down the shaft of my SC Newport from 35 to 34. How does that change affect the performance of the putter? Should I add lead tape? If I do what will it do to help the putter? I also changed the loft to 3 from 4

Nah, you don't need to do anything.

Now get out there and start draining putts!

How about putting a lamkin cord putting grip on it?

Yeah man, go for it!

And be confident that the changes you made are going to bring wonderful putting success!