Interchangeable ch/sh and k/t characters

[ololololo]

We are dealing with words that differ by only one consonant, such as, for example, in French the words "bateau" (boat), "château" (castle), "gâteau" (cake), and "râteau" (rake). 
Do they all mean the same thing?
And what about the verbs: "disait" (was saying), "gisait" (laying), "lisait" (was reading), "misait" (was betting), "visait" (was aiming)?

That's true, but we can't say from here that d is the same as g, and you can't replace d with g in all French words. 
In the case of Voynichese, this analogy is hardly appropriate, or are you trying to say that you are a great seer who knows what is written in the manuscript?