I was reading the thread about Sliding's highflow turbos and they say you have to modiy the turbo's oil feed line to make sure they get enough oil.

"Instructions are provided for the modification of 1 oil feed line and 2 oil feeding banjo bolts.

These easy modifications can be had done for under $20 at any mechanic or engineer to provide the necessary oil flow and cooling for these turbo's.

Having these simple modifications done are a requirement pre-install to insure that the turbo receives the required oil lubrication and cooling."

This is the picture.

Would this be advantageous for the stock turbo setup, or is it a waste of time?

Can the standard turbo make use of a bigger feed or are the lines within the turbo too small anyway?

BTW, I have a RB25DET NEO that is currently standard, but I am soon to do a turbo back exhaust.

Don't do it. Slides turbo's use a journal bearing as opposed to a ball bearing which need the extra oil flow. You'll flood the standard turbo with oil and most likely the excess will come out the turbo's oil seals and go into your exhaust.

As above, leave the turbo how it was designed