If you have capacity (ie you're conscious and you understand the risks/benefits, which obviously you are/do) you have to consent to treatment before they can give it - of course you can refuse it.
I can understand why the nurses seem keen to stick you on sliding scale - if they aren't DSNs someone managing what is quite a complex regime themselves will freak them out - basal bolus and sick day rule are pretty complex and if they aren't used to it they will want to follow the tick box approach and stick you on sliding scale, keeping you numbers in low teens while you have a pretty severe infection is good, but I'm not sure it's successful, they will be aiming for under 8 I would think. It would be brilliant if you can get reveiwed by the DSN in the hospital (if there is one?) and if I were you I would be asking - before making a decision on how well you were doing with the sick day rules yourself - if I had ketones & stayed in double figures I would be tempted to hand over if I was confident there was DSN support & I felt rough myself, because it's a pretty intense regime of hourly testing and big corrections & I really don't think I would be confident to do it myself (it's really impressive you are, but I hope you can get get support from the DSN to consider). Having said all that, hospitals are notoriously rubbish with mangaging type 1 for inpatients - so if you would just rather do it yourself, you might very well be much better off doing that - absolutely ask them questions and ask for DSN support.
I hope you get the required support are feeling a lot better soon.