There are two negative factors to retorquing after so long... I'm going off memory here so forgive me if either isn't completely accurate. The first is that the jackets may have hardened and could be compromised; I don't think this is very likely. And the other is that now that the bolts have sat in place for so long you're not going to get an accurate torque value for each and may not get them uniformly tightened or you may not even be able to tighten them due to artificially high readings from seizing.
Now, with that out of the way, I think you're fine to do it. Just crack each bolt loose in the correct order by 1/4 of a turn and tighten them in order in multiple passes.
Do keep in mind that it is possible that whoever did the HG last did use a higher torque level... don't go higher just because...
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