Is ther any reason I can't use a 200 amp main breaker panel on a 100 amp service if I remove the main breaker and install a 100 amp breaker on the buss do I need to lock down the 100 amp breaker any advice apriciated this is single phase residential
I can't see an issue with what you are proposing to do. I would be concerned about the UL listing though even though both of us would see no other issues in doing so. You may want to dot you "I"s and cross your "T"s to assure that you can maintain the service entrance listing. It may be up to the AHJ. It wouldn't be a lot of fun if you were shot down on a technicality.
What size conduit do you have coming into the panel? Is it being feed with AL or CU? If the run isn't all that far is it possible to replace the cable from the meter to the panel with CU sized for 150A? This would be dependent upon what the actual service drop is which may be 200a.
I made that mistake when I changed a 100a 20ckt Sylvania panel to a 100a 30ckt C-H panel and still had to add a subpanel anyway. It was after the fact that I realized that with the 1-1/4" conduit from the meter to the panel I could have used CU that would have allowed for 150a knowing that the standard service drop was 200a anyway. I too wanted a 42 ckt panel with a 100a breaker but the style main breaker wasn't available with a 100a rating. So much for 20/20 hind sight.