It's do-able. blonde to brown I mean, but going back is very difficult. You don'tget the same 'lift' on coloured hair as you do on natural and you end up with a line where the shades differ. I wouldn't if I were you, you may love it initially but will that will wear off.
i had a lovely blonde colour acheived by years of highlites at a very expensive salon then for some reason 3 weeks before i had my baby i went to a salon and went brunette it lasted four months then went back blonde but never quite the same,those pregnancy hormones have a lot to answer for.
My opinion on hair is: there are very few styles and colours that suit each person, so however boring you feel with your hair, leave it alone if it's nice and suits you. I have had very blonde hair, with a fringe/side fringe and a few layers, longish length for a few years now and the reason i havent changed isn't cos i'm boring, but cos i know what suits me.
I'd stick to being a blondie Tilly's Mum... more fun