I've got a string: (notice the spacing)

eh oh    37

and I want it to become:

eh oh    36

(so I want to keep the spacing)

Using awk I don't find how to do it, so far I have:

echo "eh oh   37" | awk '$3>=0&&$3<=99 {$3--} {print}'

But this gives:

eh oh 36

(the spacing characters where lost, because the field separator is ' ')

Is there a way to ask awk something like "print the output using the exact same field separators as the input had"?

Then I tried with sed, but got stuck after this:

echo "eh oh   37" | sed -e 's/\([0-9][0-9]\)/.../' 

Can I do arithmetic from sed using a reference to the matching digits and have the output not modify the number of spacing characters?

Note that it's related to my question concerning Emacs and how to apply this to some (big) Emacs region (using a replace region with Emacs's shell-command-on-region) but it's not an identical question: this one is specifically about how to "keep spaces" when working with awk/sed/etc.