A GUI label from a config file

I wonder if it is currently possible to have the label of a GUI element come from a variable in a config file. 

For example, A QT GUI Range block's label is

str('Power: ' + ch_1_label)

Where ch_1_label is coming from a variable config block. However, when I run the flowgraph I get the error

'UnboundLocalError: Local variable referenced before assignment' error

Thoughts

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Anish