Thanks!!
To my surprise, after just installing KeyShot6, KeyShot5 plugin on Wildfire5.0 came to call KeyShot6 instead of KeyShot5,
and it looks live-linking is working well

Then, can we select the invoked KeyShot version with any simple setting?
...For a while, still I must supply KeyShot5 data to my colleagues...
I tried just uninstalling KeyShot6, but then KeyShot plugin came to not working at all, standalone KeyShot5 still works fine though!
After re-installing KeyShot5, the plugin came to working again.
Next, after re-installing KeyShot6, the plugin came to invoking KeyShot6.
And next, after running keyshot_w64_5.3.6_update.exe, the plugin came to invoking KeyShot5 again...
...so, It looks like the invoked KeyShot version depends on last run installer version.
How the KeyShot plugin decides invoking version!? ...by any environment variable or Windows registry!?