Changing Visitor Visa Stay Length

[benjamintrevor]

My parents just got their 6 months visa.
When applying, in the cover letter we mentioned that they'll stay 10 days.

But, now I want them to stay like 30-45 days. I read in some places, if you stay more than stated number of days mentioned while applying, it can affect your next visa application.

In next applications, they can reject because you didn't keep your words first time.

Is it legit? Is there any rules/guidelines on that? Can it really happen?

[AmazonianX]

My parents just got their 6 months visa.
When applying, in the cover letter we mentioned that they'll stay 10 days.

But, now I want them to stay like 30-45 days. I read in some places, if you stay more than stated number of days mentioned while applying, it can affect your next visa application.

In next applications, they can reject because you didn't keep your words first time.

Is it legit? Is there any rules/guidelines on that? Can it really happen? It has happened and clearly stated as the reason in refusal letter.

It is an unusual reason for refusal and probably far and in-between but it can happen.

[Casa]

The issue is that the Case Worker will have assessed the visitor visa application on the information given. This would include the funds available for a 10 days stay, which may not be sufficient for a much longer visit.

Future visa applications may come under closer scrutiny as to whether the information in the application is reliable.