Hi there,
As stated above, I don't think you need to be concerned. From my past experience if the Rozzers do appear they will be entitled to inspect your shooter, worst case is that can take it away to be chronoed if offences have been committed, but they do not appear to have been so providing you don't give them reason to suspect anything (ie by hiding the gun which they already know you have) this shouldn't need to happen.
The gents who have given the advice above to take the humble approach are spot on, and it may be worthwhile informing the boys in blue that you will be fitting a mod