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Do you current have dual ring?
If so, you can get a stack election as soon as you power down switch #3. I.e. you don't need to reload whole stack.
Once master is switch #1, you replace switch #3. (Add replacement with power off, connect stack cables, then power on.)
Once switch #3 is replace, you can power down switch #2 and replace it.
To insure replacement switch join stack correctly, they should already have same IOS version installed as other switches.
In the above I assume you've replacements' configurations are "blank". You only need to change provisioning, on running stack, if replacement switches differ from switches being replaced. If they differ, you can configure the replacements' ports when existing switch powered off, and before replacement powered on, or after replacement joins stack. (NB: also if switch types differ, if you remove provisioning from running stack, a "blank" replacement should join stack as the "missing" stack number unit.)
