The only reasons for concern are
*colours and bleaches can take differently
*You are at more risk of an allergic reaction
I'm guessing you've bleached from red before - but if you havent - its a huge job!
In answer to another point, bleach
can be used on the scalp but no stronger than 20vol is recommended. I had bleach applied at a salon a few weeks ago and it wasnt long for longer than 25 mins, and I still got minor slight burns from it. I'm an ex hairdresser, Ive used stronger bleaches against all advice for years but it goes to show reactions and burns can happen at any time. Please tread carefully!
I would suggest, if you are going to do it, to use Jo Baz or Colorb4 colour removers before reaching for teh bleach, to minimise the work needed to get the red pigment out, and damage (ive just bleached black to bright pillar box red, it took time, work, knowledge and money, but the removers do help!)