If I copy a title to a new instance will the original be changed if i modify the
copy? can I save a title as a template to prevent this from happening?
Just create a new title based on the current title.
If by "copy to a new instance" you mean, right click on title in bin, and select "copy," then no, the original won't be affected by changes to your copy. If you mean dropping your title to a new (second) spot on your timeline and editing it there, then yes, your original will be affected.