XING RESTR NOT MET. INCORRECT USE OF FCU (FLT CTL UNIT).

Narrative

WE WERE TOLD TO CROSS 25 MI W OF ESL AT FL250. WE WERE TOLD TO EXPECT A DIFFERENT RWY THAN ANTICIPATED. DURING DSCNT I REPROGRAMMED THE MCDU FOR THE APPROPRIATE RWY. WHEN I LOOKED UP WE WERE PASSING ABOUT FL280 AT 30 NM W OF ESL. I TOLD THE PLT I THOUGHT WE WERE HIGH AND ASKED HIM IF HE THOUGHT HE COULD MAKE IT. I RECEIVED NO VERBAL BUT HE KNEW WE WERE CUTTING IT CLOSE. HE INCREASED THE SPD (AUTOPLT ON) TRYING TO INCREASE OUR DSCNT RATE; AND ANGLE. INSTEAD THE PWR INCREASED AS THE ACFT TRIED TO MAKE THE REQUESTED SPD WITH THRUST; NOT PITCH (SPD BRAKE EXTENDED). I CONSIDERED BRINGING THE THROTTLES TO IDLE; TURNING OFF THE AUTOPLT; AND DUMPING THE NOSE. BUT TAKING THE ACFT FROM THE OTHER PLT IN THE A320 CAN ADD MORE CONFUSION THAN IT'S WORTH. INSTEAD I CHKED THE OUTSIDE TFC THEN TCASII AND SAW NO CONFLICTS. I BELIEVE WE PASSED THE FIX 200-300 FT HIGH. CAUSE -- COMPLACENCY ON MY PART. THIS WAS A STRONG PLT AND I FELT I HAD MORE LEEWAY TO CONCENTRATE ON AND CLEAN UP THE MCDU. ONCE THE LNDG RWY IS CHANGED IN THE MCDU; THE PREVIOUSLY PLACED ENRTE AIRSPD AND ALT RESTRS DISAPPEAR. AFTER REPROGRAMMING THE COMPUTER; I LOOKED UP AND WE WERE HIGH. TO THIS DAY I DON'T KNOW WHY. SOLUTION -- BETTER XCHKING ON MY PART; NOT OVER TRUSTING ANYONE. A SOFTWARE DESIGN CHANGE OF NOT DUMPING RESTRS WHEN A RWY IS CHANGED WOULD BE WELCOMED.