Yes, it will probably not be possible to use long-range anti-aircraft missiles in the VLS version, but I think that for the defence of units the size of the Sahand, even SAMs for short- and medium-range defence as in the Shahid Soleimani FS313-01 catamaran corvette are acceptable.
My simple hypothesis, apart from internal modifications, would also include a limited increase in the external height of the superstructure and the possibility that the tubes of the launch silos would not be almost level with the deck as in the catamaran, but slightly higher, which should allow the installation of medium-range SAMs without problems.
However, the Danes to upgrade their old Niels Juel class Corvettes, installed VLS Mk-48/Mod.3 launchers for RIM-7 Sea Sparrow missiles with above-deck installation, as can be seen in the attached photos the dimensions are not exaggerated, on the contrary, this configuration there are 2 x 6 SAM missile silos + 6 tubes for gas venting.
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The Danes have placed them aft, but given the dimensions, a similar but adapted configuration where I had placed the VLS on the Sahand might be feasible.
Here in two configurations with 6 and 9 VLS
In the first 6 VLS and for the expulsion of gases create ducts connected with openings in the ship's side, openings possibly equipped with a hatch that can be opened when the SAMs are launched and then closed to prevent sea water from entering.
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In the second with 9 VLS, the additional 3 each equipped with an exhaust pipe that goes to the deck.
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But again, this is a simple hypothesis that probably cannot be realised.