Simple Q&A D&D 3.5 (by RAW) XXI

[Curmudgeon]

Step 1: change armor to a set of clothing.
Step 2: change armor back
Step 3: change armor into a different set of clothing.

Both changes satisfy the condition of being "a set of clothing".

"Different" is your own addition, something not specified in the rules. As already stated, absent such special language as "different" or "random", the singular article indicates just one set of normal clothing as per mattie_p's answer. Beyond not having any language which would allow more than a single set of clothing, the armor property of course lacks any mechanism whereby the user could make a selection if more than one set of clothing were possible. Positing a difference in clothing from one activation to another is not backed up by the rules. Magic in D&D performs as written, and never gains capabilities beyond those specified in the RAW.

A 137 11.

If you interact with (touch) the glamered armor, the DC is given by the standard formula: 10 + spell level + minimum required ability bonus.