the item required level to wear is calculated after you insert jewels / runes.
if suppose the item requires level 48 to wear with no jewel inside , it will require level 66 if the jewel is level 66 . same goes for mo'ing , it will calculate the increased item level the same way . same example : 5 MO's are increasing the level required to wear the item by 20 levels -> if you normaly have level req. 68 with no jewel inside , this will increase to req. level 86 if you got a jewel inside with req. level 66 as it will calculate those extra 20 levels to the highest value .
same goes for socketing runes . the required level to wear depend on what you got inside the sockets . if the things in the sockets are needing a higher level to equip than the base item , than the item req. level will increase based on what you put in socket .
supposed you make a crafted weapon with level req. 90 and you MO it with 7 MO's -> now it requires level 118 . if you socket a level 100 rune inside , the req. level to wear the item will increase to 128