How to copy an original rom to aply to other device

[chmod]

Hi there,

this is my first post to this forum, so, be nice...

Don't know if I'm posting to the right place. If doesn't, please redirect me and let me knoe it.

I'm wondering if there is any way of backing up an entire rom.

I live in Brazil and flashed my Samsung Galaxy i7500. Everything is working fine, but still having some issues about battery life.

I wish to ask my money back to the justice. But as I flashed my phone, sure Samsung will say I messed something up.

My plan is to ask someone with an original I7500LIII3 for a copy and aply this rom back to my phone.

Is there any how to about this?

Realy thanks for that.