The way described is the way you create multiple records on Route 53. Entering two values in the textarea separated by a newline will result in two distinct records in the DNS. This is why Amazon call it a “record set” – it is a set of records.
v=spf1 include:_spf.google.com include:otherdomain.com ~all There’s no restriction against including multiple names in a single entry; Hotmail, for instance, takes this to extremes. Note that multiple includes, or nested ones, need to stay under the limit of 10 total DNS lookups for the whole SPF check.
Dig will also do it quite nicely: dig -t txt example.com and if you add the +short option you get just the txt record in quote marks with no other cruft.