Creating a template for use with blocks

[bridges101]

How would I create a template to be used with blocks. I want to make a copy of the guest template and have my block point to the new template so I'm not making changes to the default template. I made a new template but I can't get the block to point to the new template.

[opentype]

A theme is a complete set of templates for users/groups. You don‘t call just pieces of it. If the guest sees the new theme, the guest should also see the block templates  from that theme. (Unless they are Pages templates. Those are independent from the theme.)