I am currently running a modern Deore 48/36/26 crankset with a Deore front derailleur and Deore 9-speed trigger shifters. I have never used the 48 ring so I want to remove it and then replace the 36 with a 40t ring. The resulting 40/26 crankset would be paired with a 12-34 9-speed cassette.

Can my current Deore triple shifter and front derailleur be made to work with a double crankset? Can a good mechanic set it up so that the most outward click isn't possible and I can safely shift back and forth between the middle and inner rings without fear of throwing the chain (without a chainguard)?