UPDATE ON Some results on embeddings of algebras, after de Bruijn and McKenzie, Indagationes Mathematicae 17(2007) 349-403.
Question 4.4, for the case of groups, has a negative answer, and Question 4.5 has a positive answer.  See:

[23] On coproducts in varieties, quasivarieties and prevarieties, Algebra and Number Theory  3 (2009) 847-879 MR 2587406.   abstractpreprint

As noted there, under slight additional conditions, the group case of Question 4.4 remains open.  A variant of Question 4.5 is shown there to have a negative answer, while other possible variants are noted which remain open.

Reference [20] has appeared:

[20]  Wehrung, F. -- Embedding coproducts of partition lattices,  Acta Sci. Math. (Szeged) 73 (2007), 429--443,  MR 2008m:06011.

However, a result that I described as occurring in [20], that  Self ( Ω )op  cannot be embedded in  Self ( Ω ),  is  actually proved in

[22] Araújo J. and Wehrung F. -- Embedding properties of endomorphism semigroups. Fund. Math. 202 (2009), 125--146,  MR 2010c:20077.

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