Does anyone have any idea how to seperate a beta techno 1999 crank so I can put new piston rod bearings

if you mean the big end then its a specialist job

Sure, If you have say a 10 ton press just push it apart. But you really need a whole rod kit or you are wasting time and money. Upon assembly you have to be extremely careful to have both crank halves totally lined up before you press it together. Press until you have 18 thousandsth clearance between the rod and crank. Now you have to measure how well you did lining up the crank. Biggest thing that you need is both crank halves have to be perfectly true to each other. This is where it gets fun! You need a large brass hammer to knock the halves back to true. The crank has to be as true as possible or you cannot assemble the crankcases. Once assembled if you are good(extremely LUCKY) You start the bike and the crank could magically balance itself in it`s first few rotations. Nothing to it. Very expensive if you screw up!

Far better have someone do the crank who has done plenty before. To do it properly you need to check that the flywheels and bearing journals and shafts are running true with a DTI after assembly. If its only a fraction out your engine will be down on power, vibrate and quickly wear out the main and possibly other bearings. I think most engine tuners press big ends for between £30 and £60.

Cheers