You can add the exceptions for which you don’t want to perform the redirect to HTTPS as extra conditions (not equal to that URL), like so:
<rule name="Force HTTPS" stopProcessing="true">
<match url="(.*)" />
<conditions logicalGrouping="MatchAll">
<add input="{HTTPS}" pattern="off" ignoreCase="true" />
<add input="{REQUEST_URI}" negate="true" pattern="^/noredirect/forthis/page\.aspx$" ignoreCase="true" />
<add input="{REQUEST_URI}" negate="true" pattern="^/noredirect/forthis/page-as-well\.aspx$" ignoreCase="true" />
<add input="{REQUEST_URI}" negate="true" pattern="^/noredirect/forthis/page-as-well-too\.aspx$" ignoreCase="true" />
</conditions>
<action type="Redirect" url="https://{HTTP_HOST}/{R:1}" appendQueryString="true" redirectType="Permanent" />
</rule>