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 for creating one:
Alternatively, as the format is very simple, you can create a params.ini file by hand. It is in standard INI file format with one parameter per line. The parameter name and its value are separated by an equals sign. For example: