That is an entirely different map format, apparently used by the Battalion Map Editor. Tiled currently has no support for this map format. Since it does seem to be tile-based, I imagine a plugin could be written that exports (and maybe even reads) that format.
Alternatively, you can add a C++ plugin. You’d do that by setting up a Tiled development environment (see Contributing to Tiled) and then looking at any of the existing plugins as example. I think the GameMaker: Studio 1.4 plugin is a good example because it also writes out an XML file.
Not sure where you stand programming wise but…
You might find it easier to write a stand-alone conversion program, since you want to just convert one xml file to another.
That way you don`t have to learn the code behind tiled which could end up taking longer than learning to code.
On the other hand, such a program would need to both read the TMX format and write the desired format, whereas a plugin only needs to write out the desired format.
But of course you are right it does not need to be a Tiled plugin, and a stand-alone script could be easier to set up, especially since there are libraries for reading the TMX format available in many languages.
To tell you the true, this is for something personal.
I played Battalion: Arena, an online turn-based strategy game, which got offline since April 1st, 2012. It featured a map editor.
I had make some maps when i played this game.
But it wasn’t the only game of the entire franchise, instead, just second multiplayer game of the series. After it’s launch, developer launched another offline version of the series: Battalion: Vengeance.
After datamining it’s files, i discovered that even being a single-player version, it still has all codes from multiplayer game, Battalion: Arena.
What i am trying to do is use Tiled as Map Editor and export all maps i create to format which Battalion: Vengeance can load and run to let me play.
Before you ask: they are flash games (.swf) and i am able to do such things i described here by using jpexs decompiler.
If i am able to achive that goal, i’ll be even more happier, hehe.