5job GMS discussion

I got a question about cores. My hero has a lvl 5 Ragging Blow / Brandish / Rising Rage core, but last night I found a Ragging blow / Shout / Final Attack core which I consider would be a better Ragging blow main core.

If i use my level 5 core to lvl up the lvl 1 one, would the second one make it to lvl 5?

You don't get all the exp, but you get most of it. I don't know the exact formula.
Your new core will probably be level 4.