If you are paranoid about people robbing the bank then A. Run the guild better. B. Think twice about who/how you invite...
If your whoring for members and not giving a mind as to who you invite you deserve it.

For 2 reason bringing that up as an argument against is moot. 1. The chance someone does it with mature organized people is very slim. Its not like the potions grow on trees and therefore creates a desire to run around abusing it.
And even then most importantly as in ANY mmo i'm pretty sure there will be a name change function down the road anyway... Derp.

I am in same boat, can't use potion due to gender conflict and name.

I think its a great idea OP. I think they should fix the potion (no gender change or add name change.) Its commonsense really; either would fix the issue.
Love the name card idea tho, fits traditionally very well.