Tuneable Parameters changed on xPC Target host

Dear all, I have a Simulink file running on a real-time machine with xPC. The model has several parameters which I like to be able to tune during run-time. So far I did that by hand when my laptop was connected to the target host with

tg = xpc;
tg.setparam(0,NewValue);
tg.setparam(1,NewValue);
...

and so on. These parameters are 'Constant' blocks in the simulink file and enter the model at various locations. I know that generally it is recommended not to update parameters dependent on other blocks since it causes computational overhead (<http://blogs.mathworks.com/seth/2011/03/08/how-do-i-change-a-block-parameter-based-on-the-output-of-another-block/ see here>). But their suggestion in using a data signal rather than a block parameter is not really what I've hoped for. That would make the whole simulink model way more complicated than it needs to be. Additionally, I don't want to change these parameters by hand by having my computer connected to the real-time machine and I want to use a serial communication from another machine setting the parameters. Since these parameters get update only seldom, once every couple minutes.

I tried to use an an Embedded Matlab Function within Simulink to do the same. The command

set_param(object,param,value)

is not supported by the code generator but can be circumvented by using

coder.extrinsic('set_param')

I couldn't test so far if that even works but I have two general questions.

- How can I make sure that this Embedded Matlab Function is only executed once it receives new data? - What would be the best way to tune these parameters online without external connection?