If spex_bk_sep is set, then spex_bk_order is an array of integers, one for each spex_bk_eband energy band.
Note that once spex_bk_sep has been set, even after unsetting spex_bk_sep, spex_bk_order will remain a vector in order to remember your settings, even though only the first element will be used.
When spex_bk_sep is set, use this_band and this_order to get and set the order for each band:
order1 = o -> get(this_band=1, /this_order)
o -> set, this_band=1, this_order=2