Can I change colour settings 'Working Space' after I have completed editing my photos?

Changing the default workingspace in color settings does not alter existing images.

It's just the "default".

If you really have to have Adobe RGB images, then you CAN use Photoshop's edit/convert to profile command and set Adobe RGB as the destination colour space.

You will not now recover any colour information which may have been included in Adobe RGB but has been clipped when you converted to sRGB.

Always save the RAW file, then you can go back and remake images as needed in future 

I hope this helps neil barstow, colourmanagement net :: adobe forum volunteer

google me "neil barstow colourmanagement" for lots of free articles on colour management

And to aid in your future understanding of this:

See: http://digitaldog.net/files/PhotoshopColorSettings.mp4

Photoshop CC Color Settings and Assign/Convert to Profile video

After finishing editing my RAW images

Camera Raw has its own Color Space Preference, so if you edit and open an image from Camera Raw, its color space preference setting would be used for the image’s profile assignment—not the Color Settings’ Working Space.

If your Camera Raw preference was also set to sRGB, you could use Edit>Convert to Profile to make a conversion from sRGB to AdobeRGB, but that wouldn’t affect the output without further edits. To take advantage of the larger AdobeRGB space you would have to make your color corrections in AdobeRGB and expand the color into the larger gamut.

The working space actually has no bearing on this. That's just a default for new documents and missing profiles. The embedded document profile will always override it (or it should, if you haven't messed around too much with the color settings).

What you want is Edit > Convert to Profile.

This recalculates all the numbers to maintain identical appearance in the new color space, and also embeds the new profile. You normally won't see any visual change.

That said, converting to a different color space doesn't have any immediate advantages, and there's normally little reason to do it. The main reason would be to move to a bigger color space for further work that requires more headroom. I suspect your printer specifies Adobe RGB just to avoid getting all kinds of strange profiles. If they have a standard color managed procedure, sRGB should be handled correctly too, and there shouldn't be any problems with that.

Going from a larger to a smaller color space can be more problematic. Then you risk gamut clipping if you have saturated colors that can't be reproduced in the smaller color space.

But in this case, just convert to Adobe RGB to keep them happy 🙂

Oh, one more thing: For raw files, the color space is specified in ACR or Lightroom preferences. That's how the file is encoded out of the raw converter, and Photoshop will honor that (again; it overrides the working space).