Dear Prof. Jha, 
No Ṛṣi-status required: it is not that difficult to derive yāji as action noun from yaj ‘to venerate (ritually)’, ‘to sacrifice’ (hence having a meaning equivalent to another action noun derived from yaj: yajña '(ritualized) veneration', 'sacrifice'). 
See Pāṇini’s Aṣṭādhyāyī 3.3.110 vibhāṣākhyānapraśnayor iñ ca and the Kāśikā.
If I understood correctly, Vasiṣṭha is replying to a question of king Daśaratha, so the form could probably be justified in the context of the story ;)
In addition, there is Uṇādisūtra pāda 4, sūtra ca. 124-134 (depending on the edition): vasivapiyaji...vāribhya iñ. 
Commentaries give here examples of mostly feminine action nouns, but in the case of yāji some commentaries explain the meaning, exceptionally, as an agent noun : sacrificer. Śabdakalpadruma vol. 4 p. 31 gives yāji as a masculine noun and notes that it means sacrifice, but acc. to another authority: sacrificer. Wackernagel AiG Band 2, 2 p. 301 mentions an occurrence of yāji (also in Hauschild's Register p. 190) in the sense 'offering' ('das Opfern') in Manu 10.79, but this must be a mistake for yaji which I see in all editions available to me and which, unlike yāji, gives a correct metre.  
Best regards,
Jan Houben 

On Sat, 11 Apr 2020 at 05:14, Girish Jha <jhakgirish@gmail.com> wrote:
Dear colleagues
Whether अश्वयाजि is a ऋषि प्रयोग.If not,it is difficult to derive in my view.I have not seen this usage.Please clarify.
Girish K.Jha

On Fri, 10 Apr 2020, 21:29 Jan E.M. Houben via INDOLOGY, <indology@list.indology.info> wrote:
Or, to be preferred metrically:
रक्षिताः संवृताश्चैवेत्यश्वयाजेरसंभवः ॥  

On Fri, 10 Apr 2020 at 17:32, Jan E.M. Houben <jemhouben@gmail.com> wrote:
Alternatively for the second line: 
रक्षिताः संवृताश्चैवेत्यश्वक्रतोरसंभवः ॥

On Fri, 10 Apr 2020 at 16:43, Christian Ferstl via INDOLOGY <indology@list.indology.info> wrote:
Thanks to

a private note sent by Prof. Eli Franco, I change the last pāda to:
vājimedho nv asaṃbhavaḥ, or even: hayamedhaṃ nu mā kṛthāḥ, which makes
Vasiṣṭha's words sound more archaic, doesn't it?


Christian

Am 10.04.2020 08:01, schrieb Christian Ferstl:
> And Vasiṣṭha pointed out another problem:
>
> कोरोनासमये राजन् राष्ट्रसीमाः समन्ततः ।
> रक्षिताः संवृताश्चैव वाजिमेधो न संभवः ॥
>
> “In times of Corona, o king, the borders of your reign are all guarded
> and closed. A horse sacrifice is not possible.”
>
>
> Am 09.04.2020 11:18, schrieb Christian Ferstl:
>> Lockdown in ancient Ayodhya:
>>