I own a SFH in Los Angeles and am thinking of making some upgrades-1) opening up a retaining wall that leads into the backyard and install a sliding glass door2) adding a 10x12 wood floating deckMy questions are:1) How would I calculate the increase in value for these upgrades?

( Kansas City) besides google?

After adding brokerage, transfer tax, title insurance as well as accounting for any capital expense to replace 20+ year old mechanicals/roofs etc.

An added bonus is that in Philadelphia there is a 10 year tax abatement program that allows you to significantly reduce your tax bill for new construction homes or full rehab properties. 

My only concern is adding the bathroom.

Figure out what you can rent them for (:start with what they currently rent for, and look at ads for equivalents). 

A few years ago I helped my (retired) parents buy their most recent house by directly giving them a $100k cash down payment, and they would like to leave the house to me when they pass in thanks for the assistance (it ended up helping keep their mortgage extremely low since they are on a fixed income).They are very worried that it will somehow get caught up in probate or red tape when they pass even if my name is spelled out in the will, and wanted to see about just adding me to the title or something so that there is a seamless transition without any hassle.

@Charles Morris Facebook ad, D4D, cold calling to name a few

The reverse portion is really a second process added to a regular 1031.Regarding identification -You can purchase as many replacements as you want. 

You're right that adding on personal debt will reduce your score but that may be a decent trade off compared to the costs of a hard money loan.