UNAUTH ALT CHANGE BECAUSE OF A TCASII RA.

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ARRIVING ORD ON PULLMAN 2 ARR 10000 FT; 300 KTS ASSIGNED. TA APPROX 6 MI 12 O'CLOCK AND 300 TO 400 FT. RA AT 5 NM 12. DSND RA. CAPT PUSHED OVER TURNED L. CLR OF TA AT APPROX 9400 FT MSL. I NOTIFIED APCH AT ABOUT 9800 FT IN DSCNT. APCH STATED IT WAS VFR TFC AND HE FORGOT TO ADVISE AND TO CONTINUE DSCNT TO 8000 FT. AS A RESULT WE REACHED 8000 FT AT 300 KTS AND THEN SLOWED TO NEWLY ASSIGNED 210 KTS. SHORTLY THEREAFTER; WE SOMEHOW (I THINK I ACCIDENTALLY HIT A TRANSFER SWITCH) GOT ON TWR FREQ AND WERE OUT OF TOUCH WITH APCH FOR ABOUT 15 NM. WE NOTED THIS ERROR; GOT BACK ON APCH FREQ AND LANDED WITHOUT FURTHER PROBS. OUR HABIT PATTERN WAS CHANGED I.E.; SLOW AT 10000 PRIOR TO DSCNT; BY THE RA SO THE EXCESS SPD WAS MAINTAINED TO 8000 FT INSTEAD OF SLOWING AFTER THE CONFLICT WAS RESOLVED. I LET MYSELF BECOME DISTRACTED BY WHAT I FELT WAS POOR PERFORMANCE ON MY PART BY NOT ADVISING THE CAPT TO SLOW AFTER THE CONFLICT RESOLUTION AND SOMEHOW GOT US ON THE WRONG FREQ. MORAL -- DON'T DWELL ON A SCREW-UP (PERCEIVED OR OTHERWISE) OR YOU'LL PROBABLY SCREW UP AGAIN.