Temporarily disable AWS auto-scaling group activities

In the autoscaling lingo, what you are asking about is suspending processes. In a nutshell each of the autoscaling activities (launch, terminate etc.) can be disabled for as long as you want.

It doesn't look you can set this from the web console (although it does display what processes are available), so you'll either have to use the api or the command line tools

From the cli that's just

aws autoscaling suspend-processes --auto-scaling-group-name MyGroup

and later on

aws autoscaling resume-processes --auto-scaling-group-name MyGroup

You can pass specific processes to suspend resume as extra arguments, but you probably don't need to do that.

Not the best way to do things, but works if you do not have CLI access at the moment.

to use the web console to remove all instances from an aws scaling group: Set max. instances, min. instances, and desired instances to 0;

You can make the MAX instance = 3 and MIN instance = 3 i.e. Specifying the same instance count for both min and max.

This way there shouldn't be any change in the instance count no matter what your rules are.