Tried to create 2 record set type=TXT in Route53
You would enter all the TXT values at the same time... even the one that already exists.
Example CLI:
route53 --zone example.com -c --type TXT --name example.com --values "text1","text2","text3"
Example WebUI:
"txt=ABC123"
"txt=CDE456"
See here as well: https://superuser.com/questions/573305/unable-to-create-txt-record-using-amazon-route-53
If you are adding it in the WebUI, then your text box with have multiple entries supported in quotes, one per line.
Example:
"ms=M23445345"
"v=spf1 include:spf.protection.outlook.com -all"