[Q] 1:1 backup before flashing topic

Hello everyone,
I'm going to buy a new S4 Mini, by signing a contract with H3G, so I'm probably getting a heavily branded phone. I would like to flash as soon as possible a custom rom, maybe CM12, but still I would like not to lose my hardware warranty.
Is there a way to make a 1:1 backup of all the software, firmware included? On linux I'd put something like this in a terminal:

Code:

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dd if=/ of=backup.img

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Is there a similar procedure to follow on an android phone? What I want to get in the end is a backup that, if restored, can fool my phone operator into thinking I never messed with the software (hence, not voiding the hw warranty).

Thanks in advance.