Why no, I wouldn't pay someone to cut my MB to pieces, but I also wouldn't pay someone $400 to do something I could do myself in 20 minutes for $15. This is I believe, the nature of this forum - ask for advice instead of simply paying the mechanic to do the work.
I appreciate all the help I receive on this forum, but please understand - Not everyone who owns these cars is wealthy. I am reasonably skilled in repair and have seen that the heater box is quite stout. To cut an access opening into it should not compromise its "structural integrity," and if the right adhesive is utilized, it could be re-closed without risk of failure in the future.
While I appreciate the conservative nature in the responses so far to 'taking a blade to a Benz' I fail to see why nobody has stepped up to make reply to the question of why this IS or is not feasible.
Remember, there are several pounds of glue ALREADY in the car. That MB engineers did not include an access port seems to me no reason not to consider the creation of one.