It is not possible to change the template, but you can change some of the elements of the drawing template depending on how it was set up. For instance, if you set up your 'customer name' as a draft file property and placed it on your title block using Property Text, then a simple edit of the property is all that is needed. Simialarly a tolerance block could be set up the same way or if it was placed on the background sheet, you could just edit it in the background sheet and it would then update on all sheets that used the background.
Templates are what I call a 'seed' file. They are simply opened when you create a new file and then a 'Save As' is performed to create the new file. After that, all you can do is change the content of the files you have created from it. The key is to strategically set up the stuff you may have to frequently change using the tools in Solid Edge that enable rapid change such as Property Text.
One way that I have accomplished something similar is to turn off the working sheet and turn on the background sheet. (View Tab) then delete the title block from the drawing you want to copy to. And then turn on the background and turn off the working on the template file and copy the whole drawing template to the background of the new drawing.Then turn off the background and turn on the working sheet and voila. ..hopefully that makes sense. NOTE: This will only work if the two drawing templates are the same size (ie 2 B sized drawing files)