Thank you.
I recognized what’s really demanding in my case:
I need numbered headers in two versions.
E.g.

Current bylaws | Proposed changes
|
§1 Preamble | §1 Preamble
1. Bla | 1. Bla
2. Foo | 2. Bar
3. Baz | 3. Baz
|
§2 Something | §2 Something different
|
| §2a Something new
|
§3 Further | §3 Further
|
... | ...

Any ideas how I can achieve that? Should I better forget about automatical numbering?