How to avoid the section formatting layout for same text files (scenes)?

Hi,

My novel has a set of chapters (Level 1 files), but I want some of them not to be numbered with the prefix <$R>. For example, I want the first three chapters to be I, II and III, but the fourth must be different, and then the fifth and the sixth must follow the old numeration - IV and V. However, I don’t want the real chapter four (unnumbered) to be compiled “as-is”.
Level 1 1 --> Chapter I
Level 1 2 --> Chapter II
Level 1 3 --> Chapter III
Level 1 4 --> Unnumbered chapter
Level 1 5 --> Chapter IV
Level 1 6 --> Chapter V

Is there a way to change the section formatting layout selectively according to tags, for example, or should I change the Scrivener tree structure (putting the unnumbered chapter alone in a folder)?

Thanks!