The Infantry Assault Badge was also for Gebirgsjäger. Wikipedia states "It could be awarded to members of non-motorized Infantry units and units of the GEBIRGSJÄGER that had participated in infantry assaults, with light infantry weapons,[...]" and this info is correct as I re-checked it with "Auszeichnungen des Dt. Reiches 1939-45". I don´t think that he was an infantrymen but when his power/help was needed I´m sure he had to fight in this function too. All soldiers get basic training, including sappers, signal men, medics, etc..
I doubt that such correction reg. medals/badges/orders is possible due to following reasons:
1. The country (Nazi Germany) for whom he fought as soldier doesn´t exist since May 1945. So whom do you ask for such correction?
2. I doubt that such personal "problems" can be dealed/cared for by family members. The military doesn´t play the role here which they do in the USA.
3. Such activity might be considered "Glorification of NS Germany" what is prohibited by law.
@wbfamily: From Volyn´s link we know that it were the British who made comming home difficulty for POW. They were under British custody. See also viewtopic.php?p=2166816#p2166816
Both is of course possible, that he had to surrender them to the British when becoming a POW or to hand out them to the Americans. But I´m sure he had proper papers for his release and in 1947 the US authorities didn´t have a reason to get them handed over. The war was long over, their anger towards the former enemy settled. Contrary to activities during WWII were mistreading, killings and other violations , eg. taking personal belongings and awards/medals, happened also on allied side (remember the Dachau liberation massacre, US soldiers did murder their German POW and allowing former inmates to torture and to kill them even while they were in US custody!).
IMHO it were the British who requested them. Remember that my entire family and relatives thought for more than 60 years that my grandfather fought the Americans in Africa while it were the British. Including himself! Common folk didn´t have any knowledge of English either, and many had very simple education [Eastern Austria, where I live, was until 1921 western Hungary and of course Hungarian used as official language, so all the people born before had to learn German at first, that´s visible in the letters].
Of course we do NOT know what is correct/really happened, but this variant is more likely, IMHO.
And I agree, as long as we don´t have any evidence as entry in his Wehrpass or from photos, resp. information from WAst. we can only guess what the marksmanship badge might have been.
Volyn, to be specific, the Waffenfarbe is "hochrot" not only red

There´s also "karminrot" , also called "Karmesin" or "carmine red" which was used by OKW/OKH officers, war college/academy and veterinary units.
Samples:
karmesin: https://www.ralfarbpalette.de/ral-class ... -karminrot
hochrot: https://www.bauhaus.info/leinwaende-zei ... p/20259156
Hence I think that your sample for Oberfeldwebel and Artillery is correct.