Adding additional AML parameters to the quick search?

Overwriting the default AML on general level sounds like a bit of an overkill for your use case.

1. You can use the "Default Search" column in the ItemType property relationship. E.g. you can add a filter to the state property and by default the grid will only display items with this state. I use this for ECOs so people only see stuff that isn´t completed yet. Pro: User can see the filter and remove it when needed.

2. onBeforeGet Method can overwrite AML query. I do something similar with the select query:  link 

Look at the "select" sample code below the green Chris answer. Should work for "where" the same way. I use it since years.

You can use the "Default Search" column from the ItemType property relationship. For example, you can apply a filter to the state property, and the grid will only display objects that have this state. I use this for ECOs so that people only see things that haven't been completed yet. Pro: The user may view the filter and delete it as needed.