i have no idea but why not just overwrite the tully SIGIL banner with a mudd one ?
could save you the textwork
i just gave a look at the enhanced banners subfolder (guess it's teh same with 0.53's) ..
try putting/overwriting with these two in data>banners
i've replaced Sigils
.................the fish with the crown, for mudd
.................the kraken with the Hoar , for the ironborn
.................the flower with the green hand, for tyrell faction
(so you should maybe change their banner's color into grey-white)