dabbrev-case-replace is a variable defined in `dabbrev.el'.
Its value is

  • This variable may be risky if used as a file-local variable.

Whether dabbrev applies the abbreviations's case pattern to the expansion.

A value of nil means preserve the expansion's case pattern.
A value of `case-replace' means preserve it if `case-replace' is nil.
Any other non-nil value means modify the expansion
by applying the abbreviation's case pattern to it.

This variable has an effect only when the value of
`dabbrev-case-fold-search' specifies to ignore case.

You can customize this variable.