Uwizard never repack 100% correct... If you compare original file and a rebuild file without modification you will see... make a test... In my tests I repacked Bootup_USen.pack Unmodified, and it don't works, game freeze.
To YAZ0 I'm using yaz0enc.exe from here http://amnoid.de/gc/ - You...
Use this tool to rebuild .SARC or .PACK files... https://github.com/NWPlayer123/WiiUTools/blob/master/SARCTools/SARCPack.py
If you want change the padding value... modify the line 96 with the value you want...
example: line 96: test.pack(sys.argv[1], 0x100), the value of padding is 0x100...