Adding hand pump to existing wells

Has anyone added a hand pump to an existing standard built deep well? How does it affect original set up and are there any problems that are very challenging? I would like to be better protected from blackouts that also shut off our water.

I have no experience with them, but Bison makes hand pumps which can be installed in the same casing as the electric deep well pump (at least under suitable circumstances).
https://www.bisonpumps.com/products/standard-deep-well-pump-system/

The HydroMission SlapShot deep well pump can be DIY'd from hardware store plumbing parts with minimal machine tool work:
http://www.clean-water-for-laymen.com/well-hand-pump.html
I am very doubtful of the quoted parts price of $45 (US) - that must be quite old.  Perhaps something more like twice that figure is more realistic at today's prices.  You'd still need to add in the cost of the sucker rod (1/2" nominal PVC pipe) to reach the desired depth and an actuator (e.g. a pump handle or treadle) of some sort.

I don't think either of the foregoing actually answer your questions, however.  But, they probably pretty well cover the full spectrum as regards cost.

I did.

Ingredients needed (assuming Bison pump with 1.25" inlet):
-Bison pump
-1.25" stainless nipple
-1.25" to 0.75" stainless female/female NPT reducer
-6 m of stainless 3/4" schedule 40 pipe with a male thread on one end

I have drilled a larger opening in my well cap so 3/4" pipe would fit.
I have put the pipe through the cap and secured it with the reducer.
I have put the cap back (while doing it, my electric pump main pipe was resting on the other half of the cap) and secured it with bolts.
I have screwed in the nipple into the other side of the reducer.
I have screwed on the pump.
Works the same for last 12 years.

All stainless that I use for water is 316 type. 304 is not enough rust proof. All fittings look the same like 12 years ago when I attached them.
I can add some photos tomorrow.