Can someone be a "twice awarded Combat Infantry Badge recipient" from different wars (Korea & VN)?

Yes ... best I a can tell SSgt GG-15 RET Jim Lint, as I believe the are different eras.

Subsequent awards of the CIB may be awarded provided the Soldier has met eligibility criteria in separate Qualifying Periods/Eras. For example, a second award with superimposed star on the wreath could be awarded for a Soldier who served in Somalia (3d Qualifying Era) and OEF (4th Qualifying Era).
https://www.army.mil/symbols/CombatBadges/infantry.html

1st Qualifying Era

World War II: 7 December 1941 – 3 September 1945

2nd Qualifying Era

Korean War: 27 June 1950 – 27 July 1953

3rd Qualifying Era

Republic of Vietnam Conflict: 2 March 1961 - 10 March 1975;
Laos: 19 April 1961 - 6 October 1962;
Dominican Republic: 28 April 1965 - 1 September 1966;
Korea on the DMZ: 4 January 1969 - 31 March 1994;
El Salvador: 1 January 1981 - 1 February 1992;
Grenada: 23 October - 21 November 1983;
Joint Security Area, Panmunjom, Korea: 23 November 1984;
Panama: 20 December 1989 - 31 January 1990;
Southwest Asia Conflict: 17 January - 11 April 1991;
Somalia: 5 June 1992 - 31 March 1994;

4th Qualifying Era

Afghanistan (Operation Enduring Freedom/Operation Freedom's Sentinel): 5 December 2001 - TBD;
Iraq (Operation Iraqi Freedom/Operation New Dawn): 19 March 2003 - 31 December 2011;
Iraq/Syria (Operation Inherent Resolve): 15 June 2014 - TBD

Yes. You see the same thing with veterans coming back from Iraq and Afghanistan. Two different conflicts. The regulation is often misstated when someone from one of the theaters is in an event in the other theater would qualify them.

Example: Soldier received the CIB on tour in Iraq. Soldier was then in an event that qualified them for the award in Afghanistan. Soldier should be awarded the second CIB if in accordance with AR 600-8-22, Section 2, Para 8-6a.

AR 600-8-22, Section 2, Para 8-6b(5) gives the qualifications for after September 2001. The same AR and section, Para 8-6c(12) and Para 8-6c(13) show the two conflicts sighted separately. Likewise with Korea and Vietnam (Para 8-6c(2) & (3) respectively).

Any other question with this award can be referenced in Section 8-6 of the AR.

Personally had the opportunity to attend the festivities in Grenada, Somalia and Panama, CIB, no stars.

I know several people who have been awarded 1& 2 Stars on their CIB's! I had a 1st Sgt in VN who had 2 stars on his!

Yes they can also earn a 3rd award.

My dad earned his first CIB in WWII in Germany. He was called back in for Korea and was awarded his second CIB. He as in VietNam but not combat 1958 as advisor . My brother got his CIB as Special Forces in Nam. Dad had two Purple Hearts and Rod had none. I had a Heart but was told I did not qualify for the CIB since I was not 11B but 31M Radio Carrier.

I earned my CIB in Vietnam 1979. Was assigned to USARSO NCO Academy as operations SGT/Deputy Cmdt during Operation Just Cause. Worked as 11B, all on CIB wearers were awarded their CIB, CSM, another senior VN era CIB guy and myself all received "Certificate of Participation". Where's my star?

Yes you are awarded a star to wear on your CIN.

I think it is possible to get three if you get liked up right. It has to be different wars but that is published an old easy one would be served late in WW ll , korea, and early RVN. Three different wars three awards if mos and unit line