I have done it sucessfully with moderate amounts of deflex. How far it will bend before breaking depends on how thick the wood is, grain orientation, clamping procedure, how well your splice was done, glue used, etc.
If you are only splicing one of the lams and are able, use it for the middle one, with the full length lam on the belly. Then regardless of whether you have one or two splices in there... do this when you glue all three pieces together....
Pull the handle area down onto the center post and clamp it. Now before you pull the limbs down onto the midlimb posts, put 1 or 2 c-clamps, 2" apart, on each side of the big center post clamp... clamping the three pieces of your trilam together. These will help to support the splice and keep it from breaking while the midlimbs are pulled down onto the midlimb posts. It helps.... but doesn't make it invincible