6 perfect skulls+ rare circlet

[Guest]

Hello,

I have some rare circlets (tiaras,diadems,circlets) got from hell act 4-5
I'd like to know if I can get + 2 to skills by rerolling several times a diadem or a tiara or a circlet.
The formula (0.4*[Item Level+ Character Level) implies that each time a rare item is rerolled, the quality of the rare is decreased.
1) Does it mean that I couldn't get the mod +2 skills after the first rerolling or after several rerollings ?

2) Are there any differences between diadems, tiaras and circlets ? Can they get the same mods and do they have the same odds to get +2 to skills ?

Thanks ,
Abramelin