Not an expert, but I would say these are two differents topics : the notion of resolution of a scope is based of the capacity of your scope, given its diameter, to distinguish two separate punctual light sources. Diffraction makes punctual light sources interfere with themselves and between themselves, and they appear as two superposed Airy disks. The larger the diameter, the better you can distinguish the two « centers » of the Airy disk. So the notion of resolution is already a bit of arbitrary, as there is a loss of contrast between the two are they are merging (at what point do you consider you can still resolve them ?). So the formulas you get to calculate the resolution of your scope are setup making assumptions on what you consider to be sufficient contrast between the peaks to « resolve » them.
Now, that doesn’t mean that details that have a lower size than the resolution of the scope can’t be seen : we can see the Saturn’s Cassini separation of its ring while it is smaller than the resolution of many scopes, because most of these details are not punctual light sources, but zones of contrast (Cassini separation appears as a dark ring on very bright rings).
That’s why you can still catch smaller details with high magnification Barlow lenses, and with proper process of images (lucky imaging + proper sharpening of these zones of contrast), and the better these Barlow lens are made (in terms of transmission of light, absence of optical abberations etc…
the best images you will get, whatever the resolution of your scope is.
But of courses, coming back to punctual light sources, you won’t be able to resolve double stars system for example if the diameter of your scope is not sufficient, whatever Barlow you use.
Hope this helps a bit :-)
