More time posting than coding
What will happen is on your original SATR where you had 2000 tax free then some in 7.5% some in 34.5% and some in 38.1% (depending on how much in dividends you pay yourself ) they will add your loan amounts to your basically salary and recalculate the tax as all PAYE. Then they add your dividends to the gross PAYE income and then tax your dividends (less the 2000 tax free). So yes ulltimately your dividend tax will also get recalculated which may push dividends amounts into the higher tax bands.
they then add the restated PAYE to the new Dividend tax amounts/bands to calculate what tax you should have paid and then deduct the amount you actually paid back in Jan to work out what the loan charge will be.
So simply your dividends will end up in higher tax bands as they decide these bands after your loan amount is added to your existing small salary.
Here are the bands for your info
Tax Free £2000
Basic rate x 7.5%
Higher rate x 32.5%
Additional rate x 38.1%