Yes you can change from BC b to BC e if you have required documents to proof your caste.apply with your relevant documents attach reason for change at revenue department or social welfare of your state .if authority approve your documents they will issue new certificate.

Moreover As such there is no BC-A,B,C,D,E in central reservation. But Backward class reservation is confined to respective states only.means in some states like andhra pradesh, telangana ETC . Some otherbackward castes not well developed, are further divided into some sub-castes like( BC-A,BC-B,BC-C,BC-D,BC-E) Other than SC & ST.so if you are applying to any of these state exam you will get benefitted for this certificate.