SnapGene versions 6.0 and later will allows users to create, use and share custom Feature Types - see Custom Feature Types (SnapGene 6.0 and later).
A SnapGene 6.0+ file with custom Feature Types will be able to be opened by earlier versions of SnapGene (SnapGene 5.3 or earlier) and the file will not be modified and custom Feature Types will be retained. However, if you edit a feature of a custom Type, the Feature Type will be reset to misc_feature in the Edit Feature dialog. If you cancel editing the custom Type will remain unchanged.
If you modify a SnapGene 6.0+ file in an earlier version of SnapGene then save, any custom Feature Type information will be stripped from the .dna file.