This is why I love text editor.

All Poser files share this habit; if there isn't a line referring to a node/channel/actor, that node/channel/actor remains unaltered.

Here's how I would do it (keeping in mind I'm VERY old-fashioned); I'd make the change I wanted and save as a cr2 (or maybe an mt5).  Then I'd delete everything but the material I was trying to alter.  Then I'd delete every line but the one that set the transparency.

The big trick is making sure you keep the right number of nested brackets going, and you leave the header intact (just open another MAT-pose or mt5 for reference to make sure you have the right stuff up there).

Sounds fiddly, I know.  But I love the power it gives you.

(Plus it is the ONLY way I know to create MAT-DIV poses -- which are the only way you can change an otherwise global material on just a single Actor).