Will this work?

When going from red to blue you really need all that red out and go as pale as you can, otherwise the blue will mix with anything that's left behind. If you put blue over a little bit of red it goes purple, if you bleach to yellow then blue turns green. You need to get streaks as white as possible, use a toner to neutralise the colour as well.

Good luck!

I wouldnt use Live XXL either its very hard to get rid off.I had mine all over one of the xxl reds this time last year,I had to bleach it 3 times 40% vol,and it just went bright orange,my virgin hair bleaches dead easily.Ive still got the dregs of it on my lengths and when i dye with my reds it looks duller at ends compared to rest of my hair

I haven't had too much trouble lifting the live XXLs.  I think it depends on how heavily dyed your hair is and how much heat you normally use on it.

My hair was red and black stripey, similar to yours, and Colour B4 extra strength lifted the red to honey blonde and the black to medium brown (an hour's processing time ... instructions say 20 mins, but on Cornwall's website he says it's safe for up to an hour and they're rewriting the directions to say that).

If you decide to go ahead with the live dye after as a base, do not dye the pieces you wish to bleach ... foil them and keep them separate so you can give the bleach the best possible chance to work.

And your bleached bits *will* come out stripey because of the previous colours (I still have some peachy tones in my hair O.o), so you'll have to try to get it all as light as possible for the blue flashes to work well.  And like Mattie said, toner is important in taking out all the yellows.