Note that some nominally clear finishes (without intentional coloring agent) will darken natural finish leather; so there may in fact not be a separate base layer. At one time, I used marine spar varnish, which darkened the leather for sure. It worked fine. I don't know how dark your finish is, but even Sno-Seal darkens natural finish leather to some degree.
If your tech used some sort of varnish, I wouldn't use Sno-Seal because (1) You don't know the service temperature of the varnish that he used. Excess heat could cause degradation of the varnish and the leather. (2) Sno-Seal is primarily beeswax. If you plan on using varnish (or other coating) later, it's very likely that Sno-Seal would interfere with adhesion of the varnish (or other coating). Sno-Seal also tends to fill in the leather pores. If you plan on using a different coating in the future, you want the coating to absorb into the pores. Once you've applied the Sno-Seal, it will be very difficult to remove without damaging the leather.
My current pair of boots came factory treated with some sort of coating, so I didn't add anything else. But, if I were to treat leather, I would go with a variant of Bill's suggestion: I would go with oil-based marine polyurethane, the modern replacement for marine spar varnish. Spot test over your existing finish to make sure it adheres properly. If there are no problems, you would want to demount your blades, scrape off any chipped or peeling coating, sand lightly, and coat the whole surface; several thin coatings, allowing each coating to fully dry and harden before applying the next.