How to convert a dynamic string to a fixed length string in Simulink?

Hi,

The ASCII To String block cannot return a fixed length string using stringtype(X) most likely because it is constrained by the length of the input array. However I would like to be able to convert that string signal to a fixed length string because I have a model with an input port datatype set to stringtype(50) and that cannot be changed. Using the Convert block does not work, nor does

set_param('mdl/ASCII to String', 'OutDataTypeStr', 'stringtype(50)')

Is there anyway to convert string to stringtype(50) ?

Thanks in advance,