Max will let you choose the encoding type in its preferences (under Formats). If you choose the same type of file as the original, nothing will be changed to the file except the tags you've added or changed. Never noticed any loss of quality, on the contrary.
I'm sorry. I don't want to argue, but I think you're wrong and are giving really bad advice. When using Max, bring up the encoder window. You'll see when you're "editing the tags", the encoding engine
is running.
Try this...
On a really slow Mac, use any ID3 Tag editor (Media Rage, ID3 Editor, etc...). Edit the tags and save the file. Time how long it takes (it will be near instant on even the slowest of Macs). Now do the same thing in Max and look at the encoder window. It's taking
a lot longer, roughly about the same amount of time that it took to encode in the first place.
Additionally, if you'll notice in the preferences, there's no "pass-through" option. The interface isn't supporting not re-encoding. Even if your method of selecting the same encoding settings worked, you'd have a problem doing this since the original encoding settings aren't known within the application...not to mention that there are different encoding algorithms even when the settings are the same (see LAME for example).
By re-encoding from lossy to lossy, you're lowering the quality. You may not be noticing it, but you're definitely lowering the quality, and you may significantly notice it if you use Max to re-encode and re-encode files over and over, which would be a shame to do just to edit the metadata.
There are other tools available for metadata editing which are free or cheap and don't re-encode. Additionally, since they aren't re-encoding, it's a lot quicker and more efficient. I highly recommend Max for encoding and transcoding, but I'd recommend ID3 Editor, Media Rage, or others for metadata editing.