could it be possible?

to make a mod for special moves etc
that you click on it, and the infantry forms a shield wall type thing
but i mean it would only effect like basic infantry because in offical roman tactics this is how they used to stop a cavalry charge they would link shields line two cohorts up and have one with shields up to knock the horse men off their steeds and the other cohort to finish the horsemen off

i'm just asking would this be possible, to at least knock cavalry off with shields or make them rout away for a split second?

No.

Did you mean to throw down the horsemen? And they would fight as infantry? It would be really pretty... :-)

Well, if you're playing with the BI exe modding in shieldwalls is very simple if somewhat tedious (both me and Thorlof have put up a minimod on the subject). I wouldn't give it to the Romans (with the exception of the copy-hoplite Triarii and maybe the Auxilia) though, as they're only known to have adopted very close order in very few special occasions.