You can write a custom algorithm in Java and apply it to a field configured for use in matching. To make your custom algorithm available:
Export your algorithm as a JAR file and include it in the same location as ebx.jar.
Open the Administration panel and navigate to TIBCO EBX® Match and Merge Add-on > Reference data > Matching algorithms.

Add your algorithm:
Create a new record.

Fill in the required fields and be sure to enter the full path to your algorithm.
After saving you can fill in any required input parameters.

Save and close.
Your new algorithm is available from the Algorithms menu during field configuration of a decision tree. See Task 3b: Creating a decision tree for configuration steps.