I've been doing this for quite a while.
Once you have made a blu-ray into a MKV file quality is lost and you cannot get it back. So making an MKV file back into a blu-ray is not as good as just downloading the blu-ray itself and burning it.
You keep the quality of the MKV but it's not full blu-ray. The quality is still very good though.
But after wasting quite a few blu-ray discs at £2.50 a pop (25 gig ones), I just decided to get a media player that will allow me to play 10-20gb 1080p MKV files, much less hassle.
Depending on your blu-ray player you don't need to author an MKV file as a blu-ray disc, just burn the MKV file and the player will play if from the disk, if you use a re-writable disc you can use it again.
Freemake video converter will author any file (AVI, MKV, MPG, FLV etc...) into a blu-ray with menu too. I use it to put TV series on blu-ray disc from 720p MKV's. You can get 13 episodes on a 25gb disc and keep the full 720p quality, much better than dvd.
Freemake is a free program from freemake.com