If your life position is identified by an ideology, then I guess there should never by a change of mind. But many issues are grey.

For example, I think marijuana is not good for anyone. So my life position is to oppose its usage in all cases. Throw its users in jail for 30 years! That will deter others. But rather, I see a lot of grey area in this issue. I can still keep my principles, but the solution becomes a compromise, which hopefully will convince others not to use it. But if you want to call me unprincipled, I guess that is your right.