Relative Clause in English has two forms:

1. Parenthetical:
2. Indicative:

Also known as restrictive and nonrestrictive relative clauses. It may be easier to look up information on them using these terms.

This is why it doesn’t work to add other Type 5 suffixes to a Head Noun. Likely, the Type 5 suffix is intended to be just for the Relative Clause… unless it was intended to be just for the Main Clause… and there is no way to differentiate, and then you have to consider that the Type 5 has an effect on word order which might not work that well for either the Relative Clause or the Main Clause…

Yes, you can use other type 5 suffixes on the head noun, provided those suffixes apply in the main sentence, not the relative clause.

'u' SepmeyDaq Sovbe'lu'bogh lenglu'meH He ghoSlu'bogh retlhDaq 'oHtaH (Skybox 99)

The first relative clause, not placed in the main sentence, would be 'u' Sepmey Sovbe'lu'bogh unknown regions of the universe (notice, however, the erroneous lack of a lu-). If we call that noun phrase X, then the entire purpose clause is XDaq lenglu'meH in order to travel to X. That -Daq is being put onto the head noun of the relative clause, the noun-noun construction 'u' Sepmey regions of the universe. We know that the -Daq cannot apply to the relative clause itself, because then 'u' Sepmey could not be the head noun, leaving only the word Sovbe'lu'bogh in the relative clause — no head noun available.

-- 
SuStel
http://trimboli.name