Can I change them all at once to associate with LibreOffice.
Please, edit to make question title short (like “Editing .abw files in LO Writer”. You have ample space in description to elaborate on your request. Don’t forget to mention OS name and LO version.
.abw = AbiWord file I assume?
The answer to your question relies on the availability of an import filter in Writer and rerouting double-click on an .abw icon to LO. This second action is a matter of configuring file/application association on your system. LO does not care for extension when it opens a file. It looks at content and then decides if it understands it and launches its adequante component (Writer, Calc, Draw or Impress).