Sorry for the late reply i thought you will continue your questions by email so i did not check the forums. Please find my reply to your questions as follow:
1- I still do not understand why you would change the baseline total cost? if there is a variation order you should add new activity rather than changing the baseline activity. For example, if you have one activity for concrete which equals to 1000 $ and there is a variation order for 500 $, you need to add new activity as variation order with value of 500 $.
2- You should not change the baseline. The influence schedule which contains your new events only should be changed.
3- You cannot change dates by Excel. Dates are driven from logical relationships and are not considered when importing data from excel.
I advise you to re-study the course since you are missing some basic logic in the Claims and EOT.