Is there any way to combine a scene change at the same time that I engage the wah with Exp1?
If you're using auto-engage on the wah: no. But if you're using a physical switch to engage the wah: yes. It'll be a little awkward though.
I'm assuming you're using the MFC-101 here and that you're willing to burn an IA switch on the MFC to be a wildcard switch to do this. I don't think you can have an external switch send on multiple CC numbers right now. I'm confirming that...
What you're going to do is setup an IA on the MFC-101 to send a value on both the CC# for the external controller you have it mapped to (usually externals are CC# 16 through 28) and you're also going to have it send a value on CC# 34 which is the direct scene selection controller number.
For the sake of this example I'll assume your external controller you have the switch mapped to is External 1 (CC# 16) and that you want Scene 2 when the wah is engaged and Scene 1 when it's bypassed.
Go to the IA Switch Control Change (CC#) Settings page on the MFC (EDIT : MIDI : PAGE-> (8x)) and set c1 to send on the CC#16 on Ch01 -- this is the external controller number. Then set c2 to send on CC#34 Ch01 -- this is the scene selection controller number.
Go to the IA Switch Control Change ON/OFF Values page on the MFC (EDIT : MIDI : PAGE-> (9x)) and for the IA switch number set c1 to send an Off value of 000 and an On value of 127. This bypassed/unbypassed for the external controller. Then set c1 to send an off value of 000 to selects scene 1 when the switch is bypassed and an on value of 001 to select scene 2 when the switch is engaged.
Now when you step on this IA to engage it two things happen: the external controller gets value 127 assigned to it and the scene changes to scene 2 in your preset. You just need to assign external controller 1 to bypass/unbypass your wah. When you disengage the IA the external controller gets value 0 assigned to it and the scene changes to 1 in your preset.
There are more ways to skin this cat. But that's one of them above.