Rename ChangeToOutput -> ChangeToExistingOutput

avoid confusing with ChangeToAddress

txchange.go

@@ -31,9 +31,9 @@ func (tx *Tx) Change(s *bscript.Script, f []*Fee) error {
 	return nil
 }
 
-// ChangeToOutput will calculate fees and add them to an output at the index specified (0 based).
+// ChangeToSpecificOutput will calculate fees and add them to an output at the index specified (0 based).
 // If an invalid index is supplied and error is returned.
-func (tx *Tx) ChangeToOutput(index uint, f []*Fee) error {
+func (tx *Tx) ChangeToSpecificOutput(index uint, f []*Fee) error {
 	if int(index) > len(tx.Outputs)-1 {
 		return errors.New("index is greater than number of inputs in transaction")
 	}

txchange_test.go

@@ -380,7 +380,7 @@ func TestTx_ChangeToOutput(t *testing.T) {
 	}
 	for name, test := range tests {
 		t.Run(name, func(t *testing.T) {
-			err := test.tx.ChangeToOutput(test.index, test.fees)
+			err := test.tx.ChangeToSpecificOutput(test.index, test.fees)
 			if test.err != nil {
 				assert.Error(t, err)
 				assert.Equal(t, test.err, err)