Some excellent answers here, but let me also add: depends what your priorities are for "validity". Are you trying to maintain strict counterpoint, just reasonably consistent voice leading, or just keep it sounding fairly consonant behind the the screaming Gilmouresque Strat/bebop saxophone/ambient Frippertronics solo you already recorded over the unmodified progression?
My answers to those would be "probably not", "maybe", and "probably"/"yes"/"it doesn't matter" (screaming Strat/bebop Sax/ambient Frippertronics), respectively.
Remember: Debussy's amazing music is full of stuff that isn't "valid". Ornette Coleman's (or maybe better, Sonny Sharrock's) is almost nothing but. Erik Satie made his name ignoring the rules. Listen to Ligeti's beautiful "Requiem"' or some Meredith Monk stuff... What the hell even is that? If you want a laugh, read Ralph Ellison's contemporary reviews of the "confused" music of Charlie Parker sometime. In the visual arts, read up how the Modernists like Cezanne were received in the 1870s (and by some, still today... Odd Nerdrum, an otherwise great painter if you ask me, still rejects them.)
I think the only composers who were ever usually canonically "correct" in a theoretical sense were JS Bach and maybe Palestrina, of whom I have to cop a fair degree of ignorance. Even Mozart wasn't ("String Quartet in C" that can't seem to stay in C, anyone?) And I think even Bach probably occasionally let a zelcher slip through, once he was well-regarded enough to get away with it.
The point of my half-kidding is this: a better question would be, what are you trying to do, followed immediately by, are you musically astute enough to understand the ways in which what you are doing are valid or invalid steps towards accomplishing that? These are more productive questions. (If the answer to the second question is no, don't worry, that can be fixed with dedication and work.)
Lastly, remember, in the big picture, few truly great artists are remembered for how well they followed the rules. Think about it.