Does 300mg temazepam causes liver damage in a healthy individual that drinks alcohol very moderately?

Unlikely: This is ten times the recommended dose and very ill advised. The risk of liver abnormalities at this level, however, is low. Any liver abnormalities would be more likely due to the moderate drinking than to a single overdose of temazepam. Fortunately this dose is not anywhere near the amount necessary to cause death, but when mixed with alcohol the amount needed to cause death can change hugely.