Replace Vector at indices and return a copy

[jar1]

This is what Accessors.jl is for.

using Accessors

julia> x = [10,20,30]
3-element Vector{Int64}:
 10
 20
 30

julia> @set x[2] = 99
3-element Vector{Int64}:
 10
 99
 30

julia> x
3-element Vector{Int64}:
 10
 20
 30