Glad to be of help!
I think you are right that the "death" is metaphorical. At the most I would say that it was a satirical action and accompanying poem or charm designed to reduce the honour status of the person who had insulted the poet and by doing so, force payment of the correct nature for a poem provided or to provide the correct hospitality or privileges that should be accorded to a poet according to his status in early Irish society.
The nastier satires and spells would be the Firt Filed (the poet's spell) causing blemish to the face of the individual, thereby lowering honour status because to tolerate a satire without action was to have one's lóg enech (honour price) reduced; and the powerful Glám Dícenn used to bring down a king (encompassing incantations in a specific location and conditions and a voodoo-like piercing of an effigy with thorns). I hadn't heard of the Bríamon Smethrach until you mentioned in ..so thanks for that because I learned something new too!
Do you have access to an academic library?
if so, I see there's another reference to it given in the journal Zeitschrift fuer Celtische Philologie: ZCP xxi 324 and also the Revue Celtique: RC xxxvi 24.78
In Early Irish society, the honour price (lóg enech, enechlann) was an important status measure. It affected everything - from your power to make a contract of sale or purchase or sharing of goods/work, to inheritance rights to kin-land, to the level of sick-maintenance accorded to a person, fines for compensation in case of offence perpetuated against them and payment for work performed among many other things. Basically it marked out who you were and what level of status you held and all that this physically and socially represented.
Under the law, in the case of poets, there is a legal entitlement of a poet to his duas - the payment for a poem composed on behalf of a patron. Once the poem was perfect, the price should be paid. In some cases, patrons defaulted on this and the legal means of enforcing that payment on very high status people who could not be fined according to the usual law, was to make a satire against them. The insitution of satire was one of the most powerful in early society because satire reduces the honour price and thereby reduces the lord (flaith), King (rí) in status.
Similarly, a poet whether on public business or attending feasts or on a circuit would be entitled to a certain level of hospitality for himself and his retinue (their number also assigned by his status and level of training in the ranks of the Filid)...and if this was not provided accordingly, this would be considered a great insult to the poet and hence worthy of satire.In fact the "first satire made in Ireland" is that of the poet Cairbre against Bres, the Formorian king of the Túatha Dé Danann who houses him in a little dark house, without a stick of furniture, no fire in the grate and only 3 small dry oatcakes for a meal. Cairbre then composes a virulent satire against Bres, causing his cheeks to erupt in boils and blemishes and hence his downfall from kingship as under ancient law, no king could rule if he was blemished or otherwise physically or mentally incapacitated.
As mentioned before, satire was a formal process (if done according to the law and hence legal) where the poet would have to give notification of intent to satirize, name the offender, praise the offender and specify the offence in a "warning shot" poem called a trefhocal. Then there would be a specific period in which the offending party could make restitution of give guarantee that a gesture of restitution would be made. If this was not done within that period, then a formal satire would take place and thus the honour of this person would be brought down.
For that to happen to someone of status, it would be a terrible thing and removed many of their rights and privileges, so to this end, satire was a feared and powerful tool and not something to be taken lightly.
I would think that your term of reference fits into that, rather than causing actual death.
I don't have more specific references to it, but I could recommend that for background reading, you look up the Brehon Law translations by the below authors as you might find something therein.
Prof Fergus Kelly - Guide to Early Irish Law
Prof Liam Breatnach - Uraicecht na Ríar
You could also try to look in Bretha Nemed which is the law tract on status as the poets should be mentioned therein and likewise perhaps some of their skills. Also given that the Auraicept na nÉces is the "Scholar's primer" there may also be some reference to such arts as poet's training materials. I really don't know. George Calder did a translation of AUR so that might be a place to start.
Are you working on an essay on it or just from interest may I ask? It's such an interesting topic! Prof Breatnach has published much on poets and satire so if you google his works, then you might churn up something but you will have to sort to much reference material to find out.
Try the ZCP reference if you have access to such journals. But I don't know whether the article referenced there is in German or English - the journal it bilingual.
Happy hunting! keep me posted on your discoveries there. It is fascinating!