Agree, it is a gamble not declaring mods - or not declaring any other information the insurance company might need for that matter. It’s not a gamble I’d be prepared to take.
If an insurance company isn’t provided with full risk information including details of any mods, they can’t accurately assess the acceptability of the risk to them and / or whether they would require a higher premium compared to the premium they would charge for an equivalent standard risk.
Knowingly withholding risk information to;
- get insurance cover in the first place
or
- get a premium that’s less than the insurance company would charge if they had full risk information
might technically be considered to be insurance fraud. Insurance fraud is a criminal offence which would need to be declared in future when switching insurance companies, and the existence of the offence could affect a person’s ability to get cover -either at all or at a reasonable premium.
So IMHO, it’s just not worth the risk of not declaring mods. If the existing insurance company won’t provide cover, there are plenty of other insurance companies out there to try, including those that specialise in insuring modified vehicles.