Greetings,
Welcome to the forum.
I am not a HP employee.
I would back up important data before doing anything.
You should be able to replace the Optane stick with a 970. HP specs are not always very clear. You have a M.2 socket but HP is not defining the length of the socket at this HP Support site (Link). It should be a 2280 socket. The 80 means it is 80 mm in length. This is a little over three inches from the socket to the motherboard mount point.
The 970 will be bootable.
You should copy/clone the existing 1 TB HDD HP factory installation to the 970. This method is much faster than installing Windows clean.
Doing this change creates some issues with respect to the 1 TB HDD installed in your PC.
The HP Recovery partition will migrate to the 970 if you copy/clone the HP disk image to the 970. The HP Recovery partition may not work in the future because it will be looking for a 1 TB HDD.
This means you may have to do a clean Microsoft W10 installation if something bad happens.
There are ways to avoid this.
I recommend using Macrium Reflect free (Link) disk management software to create offline backup operating system (OS) images, rescue media, and this software can be used to move the HP 1 TB OS image to the new 970. You can also use Samsung's Data Migration software to move the operating system.
HP factory OS Recovery may be compromised when you change factory installed hardware. HP may not provide warranty support unless you go back to the factory configuration.
Regards