...not sure if I understand why you would want to do that since Tru-Oil sets up hard and provides a non-porous surface. With multiple coats and several applications of gun wax, you'll have a lot of sheen.
If I understand your question, you want to use sanded in Tru oil to fill the pores and then finish with lacquer?
I do not know for sure. I use a lot of lacquer for finishes but not on gunstocks and not on open grained wood unless I am happy with the pores showing. My guess is that if you sand the Tru oil back to just what is in the pores and let it dry for a good while you could spray lacquer over it just fine. Thin coats. Let it dry throughly between coats so you do not trap enough thinner in the coating to hurt the Tru oil. You can also thin the Tru oil and spray it instead of switching to lacquer. If you are working on a gunstock that is what I would do.
I sometimes use a lacquer sealer under the lacquer and sand it off to help with the pores. But lacquer and open pored woods are not easy.
The Tru oil takes a long time but it does make a nice clear finish much like lacquer and is tougher. My last gunstock was with Brownells custom pro oil and it came out good. But I think it added more tone to the wood than Tru oil would have.
I suspect the silicone in a gun sock might soften a lacquer finish.
I don't know about lacquer over Tru Oil but I have done a couple of stocks
by putting about six to ten coats of Tru Oil on then spraying on about
ten to twelve coats of Mixwax Poly Urthane, they come out just fine.
I use a product called waterlox it's a modified tung oil, apply it like tru oil work it into the wood with your finger until it's almost dry at least 12 hrs between coats put on about 6 coats and then wet sand with 2500 grit to knock down rough spots. Apply another 6 coats and repeat until you get the finish your looking for. Can be done any where from semi filled to a glass gloss finish. Allow it to cure at least a week before final wet sand a buffing. The advantage to this versus urethane is if you ding it it can be touched up with.
Just a suggestion but you might try min-wax tung oil finish, it is not real tung oil but a type of polymer finish that will become very hard and tough after 2o or so days of curing. might give you a finish that you seem to be after. It is much tougher than true oil by far and has a warm look unlike lacquer. I have used this product to refinish the 31 very expensive 4 inch thick Koa wood dining tables in my wife's restaurant, Kilauea Lodge, and they have held up to their daily traffic very well for over 6 years now and still look good. If the restaurant owner was willing to trust me to use this finish on these expensive fine wood tables worth well into 6 figures it might just suit your fine shotgun needs too. most important thing is you must give it the needed time to harden correctly.