I know the standard plugs used are 9s. But I have a left over 4 pack of CR8EIX plugs from my previous bike and was wondering if I could use them for my 14?

NGK heat range without looking it up, 1 being hot and 10 being cold.

9 is stock and cold for summer or all around.
8 is better for cold months so this being hotter does not cause det or pre-ignition.

I forget if the threads go all the way up or there is a shoulder? You better pull the plug to match that shoulder where the threads stop. The net shows the same part number but two different plugs having the same reach but not the same threads going all the way up meaning.

So heat change yes, thread reach must match.