I replaced both 5 m0hm with 3 m0hm recently here
What you bought look fine. I used these
In terms of removing the existing shuts I wouldn't say it was particularly hard. I didn't need a lot of heat imo.
Remove as much solder as you can using wick/braid
Re-wet the joints with as low a melting point solder as you can (ie lots of lead)
Two irons works fine, make solder blobs so you have the best conductivity and just slide/flick the resistor off
You could probably do it with one iron and a massive solder blob but these are a bit bigger than where that trick normal works
I would say the tolerance for (excess) heat in this area is high plus these are passive components
Due to there being some thermal mass you could probably heat one end up, then quickly swap to the other and lift it a little. I really wouldn't recommend this tho..I'd go and buy a £10 second iron to be honest.
Putting them back is a more personal thing. I clean the pads completely of solder, add liquid flux to them and then rely on the solder on the iron to flow. Alternatively you create a blob on one pad and press the resistor into it.
You wont have enough hands to hold the resistor down (because it will move about a lot), hold the iron and hold the solder.
Mine is pulling roughly 45a without software limiting on a 52v pack (my controller was one of the locked 28a ones)