For example I want to have the horn on two different places.
I tried to had /press B on Ctrl +F and bind it but it doesn't seem to work.
Any workaround?

I still don't understand why /press b doesnot work...

Here is a workaround I did with two scripts:

Autoexec.lfs add:

/button 136 Horn
/altf 2 /run horn2
/button 157 alt_f2

Gives a good starting state: 136 is the Horn 157 will launch script horn 2 which will switch horn to 157 and then Horn

Horn2.lfs
/button 157 Horn
/altf 2 /run horn1
/button 136 alt_f2

157 is the Horn and altf2 is binded to take back control horn to 136 if necesary with horn1

Horn1.lfs
/button 136 Horn
/altf 2 /run horn2
/button 157 alt_f2

136 is the Horn and altf2 is binded to take back control horn to 157 if necesary with horn2

You can replace XYZ to whatever your control bindinf are. This trick is not limited to horn.