Would I do a wrong thing if I get the rings on the crossguard removed? Also could this sword be specified into oakeshott typology and would I get an sword of earlier period if I get the rings removed?

http://www.museumreplicas.com/webstore/eCat/s...sword.aspx

http://www.museumreplicas.com/webstore/ShowLa..._l_000.jpg

Rather than cut that one up, try looking at this longsword. I hate buying a piece and hacksawing it and run a risk of messing it up.
[ Linked Image ]

This on is at "Kult of Athena"

But if you feel you need this one, try getting it here.
http://kultofathena.com/product~item~500800.htm

I already bought this one and I'm satisfied with it, I bought it becouse I didn't had to order, I bought it at the store in a nearby town and these rings are the only thing i would change on the sword. I think that this sword could be placed in the first half of the 15th century just if it wouldn't have the rings on the guard.

It's hard to tell from the MRL photos, but it looks like those rings are in some way integrated with the guard at its center. My concern is that cutting off the rings may result in an unsightly gap.

Perhaps you could shorten the rings to stubs, which you could then shape in some decorative fashion. Another option would be to cut each ring at the center, shorten each end and flatten each tip, then hammer them around a mandrel back into the center of the guard. This would give you a small "m" or heart on each side of the guard, which might look nice, although this would entail a considerable amount of work.

Whatever path you choose, be sure to cover your blade and grip before you start. An errant saw or file mark won't help matters.

Good luck!