My 10 week old has started rolling front to back during tummy time. Do I need to transition him to arms out even though he still has his startle reflex?

Here is Red Nose information about when a baby is rolling.
https://rednose.org.au/article/what-do-we-do-now-that-a-baby-has-started-to-roll-over

Most babies will be rolling over by 4- 5 months. Some earlier, some later.
This is very normal as babies grow & become stronger.
Many babies then prefer to sleep on their side or tummy.
This is not something that needs to be stopped. It is important to make the “new” environment as safe as possible.

Has he attempted to roll when sleeping?
Is he in a bassinet or cot?
How does he go with tummy time when awake?
Is he holding his head up &/or reaching for toys?
What type of swaddle are you using?

Recommendations once baby is rolling is to stop swaddling & move to a cot…..regardless of age.
Babies need arms free & space of a cot to roll well.