I would not use LO Writer for this. Writer is intended to work on formatted files and provides a lot of powerful tools to manage the requirements for sophisticated layout.
On the contrary, A GEDCOM file is plain text with some syntax rules structuring “records” (it looks somewhat like old COBOL DATA DIVISION description with numeric level indicators.
A text editor would be better fit to the task as there are much fewer risks to corrupt the structure by implicit (= not user-caused) editing actions. It may even be possible to find editors with GEDCOM consistency checking (this is not built-in in my favourite Linux text editor KWrite, but it should be possible to create manually such a checker).
A text editor does not
- convert the file from plain text to internal ODF format,
- change the type (extension) of the file,
- require manual action to save as plain text.
Practically all text editors nowadays have powerfull search and replace features.