When setting an expression as a parameter that is meant for more than one geoprocessing tool in ModelBuilder, it would not allow changing the expression after running the model for the first time or running the model as a script tool.

Workaround

To change the expression, manually delete the second connection to the second geoprocessing tool. Once the connection is deleted, set the Expression parameter to a different query and then reconnect to the second geoprocessing tool, which is not ideal.

Steps to Reproduce