One-liner:
$ perl -pe 's/\n/\t/g; s/>//; s/\s+/\t/; s/\(-/-/; s/\)\t$/\n/' < fold.fa
abc GGCGGAGGUAGGGAGGCACGCGAUGGUAUUUCAGAGCCUCCCGAAUACAACUCCAGGGUAGGGUGUUGAAAGCGUUGGAGAUGUCUAAAGACACCGCCAG (((((.....(((((((.(..((.......)).).)))))))........((((((.((............)).)))))).((((....))))))))).. -35.80
lmn GGGAGGCACGCGAUGGUAUUUCAGAGCCUCCCGAAUACAACUCCAGGGUAGGGUGUUGAAAGCGUUGGAGAUGUCUAAAGACACCGCCAGUACCACCCCA (((((((.(..((.......)).).))))))).............((((..((((.........((((.(.((((....)))).).)))))))))))).. -29.30
xyz CGAUGGUAUUUCAGAGCCUCCCGAAUACAACUCCAGGGUAGGGUGUUGAAAGCGUUGGAGAUGUCUAAAGACACCGCCAGUACCACCCCACCCCGGGACA ....(((........)))(((((............((((.(((((.((......((((.(.((((....)))).).)))))).))))).))))))))).. -28.40
Regular expression capture groups is absolutely a valid way to do it, and probably the least hacky.
Otherwise, you would need to transliterate the
\ncharacters to tabs, but since there are line wrappings, that will be much harder.