You can set it for a whole REPL session instead of for every instance. For example, the following uses 4-digit MATLAB-like formatting:
julia> using Printf
julia> Base.show(io::IO, f::Float64) = @printf(io, "%.4f", f)
julia> 1.0
1.0000
julia> 2/3
0.6667
julia> rand(5)
5-element Array{Float64,1}:
0.4112
0.4889
0.1706
0.4589
0.7526