Thanks, Gino, for providing this information!

To do this:

1. Start any tool
2. Open Utilities > Key-in and expand that vertically
3. Type "set item toolsettings" but do not press "Enter" 
4. You should see a set of named variables for the active tool
5. You can set (or unset) any variable listed by adding an "=" and then a 1 or 0 to toggle a tickbox, a value for a field, an item number in an optionlist, etc.

 

 

 

For example, in the above tool, you could use the following series of key-ins : 

place cell icon  (to start the tool)

set item toolsettings cellinteractiontype=1  (to set the interactive option)

set item toolsettings celltypeinteractivetoggle=1  (to enable the interactive toggle)

 

 

This can also be done in the Customize dialog when making custom tools by right clicking in an empty area and adding item settings: