Can a baseline programme have actual progress data ?

Deal all:

      I'd like to know if a baseline programme can have actual progress data ? because sometimes with  a complicated  ongoing project,we need to update the baseline programme,i.e adding some milestones/activities ,adjusting or revising some relationships / duration / start and finish date and so on.

      If the project have been carried out for about 50%(actual progress) and  we have updated the baseline programme on base of the old BLP , what i presume is that i have to input all the actual data once more time, that'd be a huge  work if the number of activities is as many as 1000 or even more.

     My question is  that can i  revise the data on base of  the actual progress schedule and then assign a new BLP which include  the actual progress data ? Is there anyone having  experience  about this issue.  

    Thanks in advance  and  take this opportunity to Wish all of you Merry Christmas and Happy New Year.

   Shiguo