Here I would try to modify render styles as defined in default.render.xml at around line 5053 - check out the minzom switches, that will probably do the magic here
<!-- Railroad, public transport -->
<switch hidePOILabels="false" textColor="$railwayPOITextColorDay" textWrapWidth="25" textHaloRadius="$textHaloRadius" textBold="true">
<case minzoom="17" tag="public_transport" value="platform" additional="disused=yes" textColor="#999999" textSize="12" textOnPath="true" nameTag="">
<apply_if nightMode="true" textColor="#dddddd" textHaloColor="$publicTransportModeStopTextHaloColorNight"/>
</case>