This is not possible with the JForex client itself:
You cannot modify a running strategy's parameters directly (using only the client's possibilities). You have to create a kind of event listener within the strategy that continuously and frequently checking/reading something (an xml file, for instance), and processing the file's content. With this you can modify the parameters on the fly.
So at least from the strategy parameters point of view, you should consider some extra coding within the strategy.
The JForex-SDK maybe a better choice, instead of the client:
You can run the Historical Tester as a java application, you can run your strategy as a java application, and you would be able to synchronize the 2 separate java programs, to update the current strategy parameter set.
More details on the SDK can be read
here.