sequence numbers are allowed for manual edits. I cannot think of a way to do this without customization.
There are preferences to control sequence number generation and validation...but I guess your use case is different.
From structure manager documentation
"Find numbers are automatically generated according to the scheme defined for your site with the PS_new_seqno_mode preference. The default scheme increments the find number by 10 as each new component is added."
@12131444: Check the value of the preference 'PS_new_seqno_mode'. I have imported one assembly from NX and it shows the 'Find No.' (earlier known as sequence numbers) correctly as 10,20,30 etc.
You can also edit the Find No. of multiple components at once using live excel integration.
Testing: NX 10 | NX 11 | TCIN
TC 11.2 | TC Vis 11.3 | AWC 3.2