list manipulation - Subtracting from a specific column

I have a huge list with huge sublists of the form

list={{a,b,c,d},{e,f,g,h},{i,j,k,l}}

I am looking for a way to manipulate these sublists based on the positions of the elements. Something like

list/.{j_,k_,l_,m_}->{j-1,k,l,m}

but without having to write the whole pattern. Is there any way to specify such manipulation based on the position of the element? Something like

list/.#[[1]] & -> #[[1]] - 1 &

that would work?

Answer

You could use: MapAt:

MapAt[ # - 1 &, list, {All, 1}]

{{-1 + a, b, c, d}, {-1 + e, f, g, h}, {-1 + i, j, k, l}}

or Apply at the first level (shorthand @@@) (see also SlotSequence, shorthand ##n):

{#1 - 1, ##2}& @@@ list