What about this implementation:
"You can also make a Bladecraft check when using a technique to retain a previously granted tag. If the technique would have granted a tag of the same type as the tag you are retaining, the retained tag replaces the tag you would have been granted. If the technique does not grant a tag of the same type, you retain the tag in addition to the new tags granted by the technique. The base DC for retaining a tag is 15, +3 for each tag the technique normally grants, -2 if the technique would have granted a tag of the same type. Note that, as this use of the Bladecraft skill is always in combat, you may not take 10 when attempting to retain a granted tag."
So with Basic techs, you have DC 16 or 18 for 1 or 2 tags; Moderate techs have DC 19 or 21 for 2 or 3 tags; Advanced have DC 22 or 24 for 3 or 4 tags; and Expert are always DC 25. That seems quite straightforward - depending on your build & Form, it's probably not automatic, but you should make it more often than not.
I like this for a few reasons. First, I had been worried that it was easy to move down a level of complexity in technique, but very difficult to move up; this makes it straightforward, though you still have to be smart about it. Second, you'll never get more than 4 tags this way, so you don't have to worry about anything breaking. Third, it makes using Advanced & Expert techniques much, much easier on the player.
In looking this over, I noticed that I need to edit the skill tricks for the tag revisions. If I use the above implementation, Exotic Grip would be replaced by a skill trick which lets you take 10 when retaining a tag.