I've been on the debadging fence for over a year now and I think I'm gonna finally go through with it.
Every mod I have made so far is 100% reversible and I want to continue with this.
I know that "G35" and "Infiniti" badges are available to order and install, but do these come with any sort of template, or anything else to ensure that they are being put into place in just the right spot?

They may.....
But I rebadged my last G with measurements from another G.

It looked fine & was never an issue when I sold it.

The spacing between the letters will be okay as they are stuck on to the holding tape with teh correct distance between the letters, however the alignment and level of the badge is dependent on your hard work.

I work at a body shop. and can tell you rebagding will be easy!! The "G35S" or Non S Badge, come on a small template. and it foloows the line of trunk edges, so thats a no brainer to reinstall. only the other bagdes like the Mt Fuji, and the "Infiniti" letters come stuck on tape. like the guy above stated. those are up to you to align and center. then stick um on. other than that it's cake!

Also since you had your bagdes on for a while now. you may see some shadowing or light scracthes. depends how you take off the glue. but a fast swipe with a buffer machine takes care of that if you end up with some light scratches! good luck man!