Taking the phone apart as it was designed should not void the warranty. they do send parts out for customers to exchange them ??
As for returning, it’s a legal issue. if you send it back they have to do something.
In the UK you have 14 days to say you are not happy and are going to return it, then another 14 days to do so. I’m sure the EU is much the same.
I want to return something bought online.
"You have the right to cancel at any time from the moment you place your online order, and up to 14 days from the day you receive your goods. This is sometimes referred to as a ‘cooling-off period’.
You need to notify the retailer of your wish to cancel your order within this time period – by email, for example.
You then have a further 14 days from the date you notify the retailer of your cancellation to return the goods."