If you cast beacon of hope and there are undead within the 30ft range, can you affect them and then cast cure wounds on them to deal a full 30 damage (3d10) to them?
Cure wounds has no effect on undead, as stated in its description.
This spell has no effect on Undead or constructs.
You might be confused with the previous edition positive-negative energy system, where you can deals damage with healing (positive energy) to undead. 5e does not use this system anymore.
You can target an undead with beacon of hope, but it will have no effect, as the spell description says. Even if your DM misses/ignores this part, it will only maximize the healing rolls it received.