Light switch during flowering

Nothing Will happen of the bulbs/lights are the same

Like UV said, the benefit, if any might be reduced due to employing it late in grow cycle. But, compared to a 165w light it should do 'something' even this late. 165 is WAY underpowered for a 4x4. The concern here is that your last light was so underpowered, the plants may not be ready for the intensity of the new light. What i wrote below is a good start, but if the plant wilts or otherwise tries to minimize its surface area, the light is too powerful and needs to be reduced further. Your next grow cycle will more likely adhere to what is written below, but still need some fine-tuning. Every garden has different local variables that make "max" DLI different from you to the next person, too. The SE5000 produces 1400 umol/s PAR at 100% power. Withotu complicating things, the percentage of power is nearly 1:1 correlated with umol/s PAR production. e.g. 50% power will be ~700umol/s PAR, give or take an irrelevant amount. These are ballpark values - i even rounded down 10-20 umol/s for your light as an example. These are good targets that most likely slightly overshoot what you need. You will need to observe and react to how the plant grows from there. That is your guide to fine-tuning power of light. The hanging distance should be about best coverage from end to end of canopy. A light meter or even a phone app is sufficient to determing proportional intensity relative to center reading. Minimize difference from center to edges as best you can but don't sacrific overall intensity. Probably anywhere from 12-18". You can also use more electricty and a bit more hanging distance from canopy - a bit more wasateful but the plant can use the extra light it adds to the corners/edges etc. May not be worth the cost, but each to their own on that. You want 800-900 ppfd which is roughly 80umol/s per sq ft (861 PPFD). 1400 / 80 = 17.5 ft max covrage for 12 hour operation. If you only run autoflowers, you can cover 150% more over 18hours (proportional to hours). So, in a 16sq ft tent, you may want to start around 90% power and go from there. Vege will be 67% of that, or 60% power is a good starting point. Since you are in flower, start at 60% and then as stated above, observe and adjust. Hopefuly 'some' vege growth remains or it's more difficult to guage how much light is given. IF no vege growth remains you have to look for light damage in the top colas. Whatever you work it out, you can start at 67% of that value in vege next cycle. If it was fine-tuned for 12 hour operation, it will be proportional to 18 hour operation. Easy math and consistent/predictable results from there. If this is an autoflower, same process as above.. in a 4x4 tent with 18h light cycle i'd stick to ~60% power to start and go from there based on what you see. This light 'could' run autoflowers in an area as large as 23-24 sq ft. It won't be a perfectly square shape because the diode distribution causes a bit more spread perpendicular to the light bars than parallel to them. Maybe 5' x 4.5' give or take a few inches either way. if you grow photoperiods, it's better to work backward from 12 hour requirements.. e.g. no more than 17-18 sq ft of coverage. By maintaining the same hanging distance, when you switch from vege to flower it's just a matter of changing the power of the light and nothing else needs to be adjusted beyond normal (obviously you keep raising the light relative to vertical growth of plant). 18h to 12h requires 150% of the power you gave before. or going the other way 67%. It is proportional to hours and area of covrage as long as only 1 of these 2 factors change.

if you giving the same DLI. noting will chnage. if you giving way more. then its going to need time to adapt or it may burn.

So late in the game it's not going to make drastic change, it is going from a 165w to 480w so you will need to readjust your height/intensity, get a feel for how much more heat it will bring.