Templates ready-made

how may I get ready-made templates for synfig source file for editing and changing

Hi and welcome here :slight_smile:
You will have to be a bit more specific!

There are already quite a few synfig source files in this forum that you can directly reuse and modify.

For a more advanced “template engine” I created a plugin that uses synfig templates to easily replicate some text transformations (but its principle could handle any layer and keyframes Synfig supports): GitHub - berteh/synfig-import-labels: Generate Kinetic Typography (artistic subtitles) in Synfig, 2D OpenSource Animation Studio, or simply import your timings and labels (/subtitles).