The current values of the template parameters are stored in the file [path-to-Joomla]/templates/[template-name]/params.ini
If your template has parameters and you intend to create an installer package for it, then you should add this file to the <files> section of the templateDetails.xml file.
<files> ........ <filename>params.ini</filename> ........ </files>
The installer will ensure that the params.ini file has the correct ownership and permissions and so is writeable.
The params.ini file distributed in a template installer package can actually be empty as the default values of the parameters can be set in the <param> elements in the templateDetails.xml file. The presence of the empty file during template installation just ensures that it is writeable. However, if you want to distribute a params.ini file with the default parameter values set in it, this is a simple procedure:
Alternatively, you can create a params.ini file by hand as the format is very simple. It is in standard INI file format with one parameter per line. The parameter name and its value separated by an equals sign. For example