The only possible GSP to GST conversion we know of is to export Giza Specifier projects (*.gsp) and create templates from it (*.gst). No other such conversion is known to us, and 20-20 Giza Studio is the only program that fits for this conversion.
Convert Giza Specifier project file to Giza specifier template file.
We found one software available in the database for this conversion.
Microsoft Windows software - convert gsp to gst on Windows
A sales and planning tool
Convert from gsp file format
The table with program actions contains information about what each program is capable of doing with their files. This may be a good pointer for further searches for certain file conversions and help you find the converter you are looking for if our search result is insufficient for you. However, it is far from perfect and may sometimes show results which are not really usable because of the nature of the software handles the files. So a conversion that appears as possible, just because of matched actions, may in fact not be possible.