Hi Dominique, I hope you have at least a little regular expression and database skills..
The easiest way to migrate your old shortcodes is export your database and replace all shortcodes with a regular expression like this
RegEx: <a[^>]+href=([””‘])(.*?\.gpx)\1[^>]?>\s?</a>
Replace: [sgpx gpx=”\2″]
(tested with Notepad++)
and restore the new database..
This regular expression will replace all links with a href that ends with .gpx with the new shortcode (it might be optimized)
You have to know, this is a risky operation and I suggest to keep a copy of the original database!
Don’t worry about the cache, the plugin is fast even without cache.. the only (very)slow process is to download the file from an http url, this thing depends on your hosting internet connection.