You must do as you see fit, if its not broken why alter!
I was on Lantus and Novorapid but my BM's were sky high after coming out of hospital (admitted with BM 59.6) my GP recommended switching from Lantus to Humulin I (remaining on Novorapid) and he split my dose times of Humulin I (was once daily on Lantus) told me to inject Humulin I twice daily 12 hours apart
Touchwood things are improving
Like I said argue your case, if they do change it get them to document that you can switch back if you see/feel any deterioration