The Data-migration-tool does not come with such functionality out of the box (and I guess it won't ever have) for obvious reasons not to mention the advantages and features you will loose if you switch from EE to CE.
But leaving this aside and focusing on the technical question, if I were you I would try to extend the tool to do what I want.
How? you may ask.
The data migration tool transfers data from a source database to a destination database and it uses a set of config files where you can specify in what order, what data and how you want your data to be transferred. That is all it does.
By default it comes with 3 modes that need to be executed in order (if you are planning to do a full migration):
Settings: Migrates the system configuration and website-related settings
Data: Migrates database assets in bulk like catalog, customers, orders...
Delta: Migrates incremental changes (for example, orders and inventory)
This said, I would start by creating the set of config files needed using the ones already there.
Then, I would first focus on migrate only settings
.
Once I'm happy with the results, I would try to migrate data
, commenting out the steps I don't need, for example <step title="Log Step">
or <step title="VisualMerchandiser Step">
(it does not exists in CE).
This does not pretend to be a step by step guide (I'm afraid, I don't even have an environment with a 1.14.3.1 database right now to try myself) and of course it will require a lot of trail and error until you get the expected result, but the good news is that is possible :)
Hope it helps.
Important: remember to backup your databases (specially source db) before you start, so you can perform as many tests you need with the confidence that you won't loose your information.
Further readings: