It might be a worry if someone is doing stuff unilaterally without at least talking to a few people about it. With only 8 units, it can’t be too hard to quickly check that everyone is happy to have a new keypad installed. If your committee has approved the work and someone on site has the skills and enthusiasm to save everyone some delays and money, then let them, so long as it is not something that requires a license. A standard strata insurance policy should include cover for volunteers.
Where I am, there are people who check and change globes in all the public lighting and make other minor repairs that stop short of the sort of thing that needs an electrician. Others do some gardening that lets our gardening contractor’s allotted hours be used to better effect. Some volunteer to re-oil the outdoor furniture and playground timbers. I split timber for our communal pizza oven and recently worked on constructing beds for our community garden, which avoid the cost of having them put together by someone paid. The OC only had to pay for materials.