General purpose theorem provers provide sophisticated proof methods, and become valuable tools in, e.g. formal software development. Of particular interest here are proof systems with the LCF architecture, developing large theories from a small logical kernel, because this approach simplifies the validation of derived results. On the other hand, such provers often lack some of advanced structuring mechanisms found in specification languages. This thesis firstly gives a formal foundation for a seamless extension of a logical framework by similar mechanisms, and secondly presents an elaborated case study in the LCF-style theorem prover Isabelle, employing the introduced concepts of morphisms and instantiation of theories in-the-large.