remark-heading-shift 
This plugin increments headings by shift. It guards against shifting too far backwards or forwards.
shift defaults to 1, it can be a positive or negative value, it will never shift a heading past 6 (because h6 is the smallest HTML heading) in case of a positive shift, or lower than 1 (h0 is not a valid HTML heading) in case of a negative shift.
For example, the following markdown:
## foo
#### bar
##### baz
Yields:
(shift=1)
### foo
##### bar
###### baz
(shift=3)
##### foo
###### bar
###### baz
(shift=-2)
# foo
## bar
### baz