K3 RX ANT clarification needed while on XMIT

[Dennis KB7ST]

S/N 4335 (so I'm new) with KVX3 installed.  I like to switch between two antennas when checking the HF beacons or even before calling someone to help determine if one antenna better than another.  I'm mostly doing this with my end fed antenna into the T1 auto tuner and a 25-foot vertical mast fed with 450-ohm line into the RX ANT (The T1 will tune both end fed and the mast on all bands but 160M when either antenna is used on ANT1.)

 I understand that the end fed tuned with the T1 ought to give a stronger signal than the untuned mast antenna, but there are times when the signal on the mast is stronger, typically at the lower elevation angles on some DX stations.  I'm researching antenna switches (the 2005 QST article, MFJ and the like).  I have a four-position Daiwa CS-401 coax switch from the 1980s, cleaned up with tuner spray, but I'm getting problems at times where the T1 will report significantly different tune parameters with the Daiwa inline and with the Daiwa taken out.  Like SWR values higher with the Daiwa inline.  What would be nice if an antenna switch that would allow me to use a 'main' antenna for transmit and then allow me to switch to RX ANT to check the other antennas not used for XMIT.  (I have the K3 / 10 watt)

While I do some more research on switches, tho, will I damage the K3 if I inadvertently punch the RX ANT button while transmitting on ANT1 (no sub-rcvr here)?

PS--while checking out the issue with the Daiwa switch, I discovered that some jumper 50-ohm BNC-BNC cables I recently bought have intermittents in them when wiggling the BNC connectors.  I did that when sweeping the jumper cables with the AIM4170C analyzer and was startled to see that happen.  I've been using them between the T1 and the K3. Confirmed it with a DMM so they will go back to the vendor.