Hi Mustak,
There is no way to run TestComplete with parameter that disables a specific extension. However, you can disable the extension manually in the TestComplete IDE.
If you want to make TestComplete not to try to work with a specific application as with open application, just run this application with the '/NotOpenApp' parameter. You can find more information in the
Open Applications - Overview help topic.
Also, you can set up a process filter in your test project in order to specify which exactly processes should be processed by TestComplete as Open applications. Information on this possibility can be found in the
Project Properties - Process Filter Options help topic.