With your current mark-up style (as shown in the original posting), all you would need to do is to add two statements to the start of your file, e.g.
. . . .
and create a file called formats.mml that contains DefineTag statements listing exactly the styles that you've used to mark-up the text and that correspond to the catalog entries in your template, e.g.
Then in your template file that already has the predefined styles, File > Import > File and select the data file.
When FM imports the MML file, the included formats.mml file tells FM that the tags already exist in the template and to apply them to the content as it comes in. Note: if you have many of these source files using the same template, you will only need one copy of this formats file.
Note: to separate paragraphs (if not tagged with a preceding <p> or whatever), you must use two or more consecutive return characters, so this might be another minor modification to your input stream depending upon the tagging consistency.
Any "transformation" for your content appears to very minor/trivial from what you've shown so far. Otherwise, I am not aware of any other method of getting the contnt in AS IS without some work up front to transform it to a format that FM can decipher.