Thanks for your question.
Your sample string is
F0 42 30 7E 41 11 00 00 01 0F 00 F7
where 0F is the variable part. So in MIDI Designer that would be substituted for the V. Strip off the F0 at the beginning and the F7 at the end to get:
42 30 7E 41 11 00 00 01 V 00
and the variable bytes should be one. So it looks like this in MIDI Designer:

Which then produces output like this in MIDI Designer:
Message Out: Length=12: F0 42 30 7E 41 11 00 00 01 42 00 F7
Message Out: Length=12: F0 42 30 7E 41 11 00 00 01 41 00 F7
Message Out: Length=12: F0 42 30 7E 41 11 00 00 01 3F 00 F7
Message Out: Length=12: F0 42 30 7E 41 11 00 00 01 3B 00 F7
Message Out: Length=12: F0 42 30 7E 41 11 00 00 01 36 00 F7
Message Out: Length=12: F0 42 30 7E 41 11 00 00 01 30 00 F7
Message Out: Length=12: F0 42 30 7E 41 11 00 00 01 2D 00 F7
Message Out: Length=12: F0 42 30 7E 41 11 00 00 01 28 00 F7
Message Out: Length=12: F0 42 30 7E 41 11 00 00 01 25 00 F7
Message Out: Length=12: F0 42 30 7E 41 11 00 00 01 21 00 F7
Message Out: Length=12: F0 42 30 7E 41 11 00 00 01 1A 00 F7
Message Out: Length=12: F0 42 30 7E 41 11 00 00 01 17 00 F7
Let me know how if that solves the issue for you, please. Thanks and sorry for the delay.