Something like this should do it for all the fly in animations as long as
they are not triggered:

Sub MakeAllAppear()
   Dim oSld As Slide
   Dim oShp As Shape
   Dim oEffect As Effect
   
   For Each oSld In ActivePresentation.Slides
       For Each oEffect In oSld.TimeLine.MainSequence
           If oEffect.EffectType = msoAnimEffectFly _
               And oEffect.Exit = msoFalse Then
               oEffect.EffectType = mosanimeffectappear
           End If
       Next oEffect
   Next oSld
End Sub