I would try the following: On ITO6 I would download all customer specific templates (that do not exist on OVO8). You can use the opc_adm GUI for this. (Actions -> Server -> Download configuration). (I cannot find VPO6 documentation on openview.hp.com, but I assume this is available in the admin gui). As download dir specify /tmp/templ6
Tar the download files: cd /tmp tar cvf templ6.tar ./templ6
Copy the tar-file to your OVO8 server (in /tmp; BINARY TRANSFER mode when using FTP).
On the OVO8 server: cd /tmp tar xvf templ6.tar opccfgupld -add /tmp/templ6
This will only upload templates that are not yet available in OVO8.
If you do want to upload templates that already exist, you will overwrite the OVO8 version with your ITO6 version if you specify -replace i.s.o. -add.
I wonder if ITO6 already has template groups
As a backup, make a full config download of your OVO8 server (select all but Actions/Commands/Monitors executables) before uploading anything from 6.
I never used opctempl. Is it available in ITO6? From the OVO8 manpage it seems it can download just 1 template at a time.