list substitution problems

I have a long list here:

listA=list(P1 P2 P3 ... Px-1 Px Px+1 ... Pn)

for a given Px, I want to substitute Px with 2 new elements Px1 Px2  :

ListB=list(P1 P2 P3 ... Px-1 Px1 Px2 Px+1 ... Pn)

I know how to do it using "reverse()" function.

But based on SKILL Language User Guide, reverse() can generate a lot of memeory.

Is there a more efficient way to do this? I don't care if it is destructive or nondestructive.

Here is my code using reverse():

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listB2=rplaca(member(Px listA) Px2)                                     ;listB2=>list(Px2 ... Pn)

listB1=reverse(rplaca(member(Px2 reverse(listA) Px1)             ;listB1=>list(P1 P2 P3 ... Px-1 Px1)

listB=append(listB1 listB2)                ;ListB=>list(P1 P2 P3 ... Px-1 Px1 Px2 Px+1 ... Pn)

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