It's easy ...

Use APK TOOL, decompile you're MMS.apk and go to res/xml and open mms_config.xml ... then edit this line "<int name="smsToMmsTextThreshold">4</int> Change this to 100 !
Phone: I9105P NFC
Rom: JB 4.1.2
Status: Rooted

"A winner is a dreamer who never gives up !!!"