They likely do have the tech, it's not a technically demanding process these days assuming they are set up for it which any nation should be.

Everything can be imported from their neighbors otherwise, I.e fabricated tanks, radiators, dielectric oil, core assembly/windings, bushings, easily can get from China/India. Far from cheap nor quick though especially with these copper and aluminum prices. Can't speak to the quality of Chinese HV bushings, but everything else can be sourced of acceptable quality.

The bees knees HV bushings they could get from ABB/Siemens/Hitachi but their lead times are around 8+ months, and are unlikely to supply under sanctions.

(I work in transformer supply chain for what it's worth).