A note's type may be converted to another:
Before conversion, a revision is saved automatically, so you can restore the original or recover any missing elements from it if the conversion produces undesired results. Read more about Note Revisions.
Markdown notes can be converted to Text Notes with negligible loss of formatting fidelity.
To do so, go to the note menu → “Advanced” and select "Convert to Text Note".
To convert a text note to Markdown, go to the note menu → “Advanced” and select "Convert to Markdown Note".
A note type conversion can also be performed on an entire subtree or a set of multiple notes using Bulk Actions.