ECO usage issues need you help

[Altera_Forum]

Hello all: 

 I'm using ECO to modify my project manually. As attached file show, signal "|SEP2MCS|TDC_VJ:inst14|tdc_ctrl_set[0]" feeds into ALUT from DATAC, and "|SEP2MCS|SEP_TDC_7ch:inst13|inst19" feeds into ALUT from DATAD. I want to exchange these two signal path, in other word, "|SEP2MCS|SEP_TDC_7ch:inst13|inst19" feeds into ALUT from DATAC, and "|SEP2MCS|TDC_VJ:inst14|tdc_ctrl_set[0]" feeds into ALUT from DATAD.  I can change it, but i don't know how to modify the LUT equation?   Or, can i constrain it as above comments in QSF file, instead of using ECO? So the QII can process it automatically!

[Altera_Forum]

PS: Because i don't want to change the logic function, so i should need to modify LUT equation when i exchange these 2 nodes path. 

 The Carryout equation and sumout equation should show the logic functions, but user can't modify them directly. They should be modified thru modifying LUT equations.