take an CUSTUMIZE.XML from your custpack package, create own custpack folder, inside make folder named tpa, inside tpa make a folder named preset and finaly make another folder inside preset called custom and inside custom just place your Custumize.xml or you can place all files from custpack package if you need it..

then connect your phone, take flash files if you need to reflash, and then mark "customize file system" and in drop down menu choose own_custpack.

Now you are ready to press Flash ;)