Just to let you all know, that if you assign a variable by reference; it’s as stated a variable and not a function or class….
The reason being is from research found; it’s a reference point by variable….
So for example:

Will make the data in $xoopsTpl, change when anything in $tpl is changed….

How can it be referenced, if there is no variable associated with the transaction?

This implies to use the $handler as a reference point… If you change $tpl how would it be sent into a function to change a variable, same within classes…..

Your second assignment of $tpl destroys the object variable $xoopsTpl is still pointing to.
Do unset($tpl) before making a new assign.
I do not understand your third part of the post.

First argument is correct, I don't understand where you're going with the others. Maybe you could explain better or use other translator.