Getting custom IVR permenent

I built a simple IVR and have it do TWO things. 1) announce a message and if no button presses, disconnects. 2) if a “hidden” number button is pressed it will send you to the *98 built in VM main menu. Where the end user can then enter an extension and password to check their VM from anywhere. I just need to know how to make the custom IVR permanent. was able to get this working but only by updating:
/etc/asterisk/extensions_additional.conf
I could not find a way to override this in: extension_custom.conf
Where (if any) is the right place to put this IVR. When I update another incoming DID the changes are overlaid. So I am thinking it needs to be in a custom.conf of some kind. Perhaps someone here has done this before ? I’ve googled a good bit and read the Asterisk 2.6 PDF manual and have not figured this out yet. Any tips or help is appreciated. If there is a good manual or other resource, I am willing to go do some reading.

extensions_override.conf

If you’re posting to a FreePBX forum, have you considered creating this IVR in FreePBX?

Yes, I will try that. Thank you both for the replies.

I did consider using FreePBX. I hit the IVR bug in 2.11 and then fell back to 2.10 and all it well there. Thanks again fellas!