Assuming I need to download an npm package, is it possible to override the declarations (.d.ts) of the package itself?

By creating a .d.ts file with the new types, in the main project folder I can't override the package's types. The only way to enable my types is to go and manually edit the .d.ts files of the package itself.

--- Example of the problem ---

The package I'm referring to has this declaration:

declare class FooClass<T> {
  get foo(): T;
}

The declaration is very flexible on typescript projects and I can easily handle it:

const fooInstance = new FooClass<boolean>();
console.log(fooInstance.foo);

Suppose, however, that I'm using a Javascript project (and I care about types). In that case I can't specify the type of FooClass between the brackets:

const fooInstance = new FooClass();
console.log(fooInstance.foo);

Therefore I create a file foo.d.ts:

declare class FooClass {
  get foo(): boolean;
}

However foo at compile time will not be considered boolean.