I don't believe mixing both fluids for just a few days can cause any damage. Just don't quote me on that...
What you can freely quote me on - Is that I replaced the PS filter at the same time as changing over to MB PS fluid (honey color if I remember correctly). It has been about two years now and the system preforms as designed.Beautifully.
Furthermore, after reading about reconditioning old (german) seals , I added a few drops of brake fluid to the mix and a little while later , total happiness ..... - Away went the leak in the steering box!!