nAma smaraNa of any chosen deity is possible, as long as it is done with devotion and love for the beloved. These are the only two specifications listed in the shAstras propagating nAma siddhAnta. Shiva keshavAbheda is an important aspect of dAkShiNatya nAma siddhAnta and this has been demonstrated effectively by Sri Sridhara Ayyaval. There is abundant pramANa for the glory of shiva nAma smaraNa:
nAmno.asti shaktirshambhoryA pApasamharaNe dvijAH |
tAvat pApAni kartuM vai shaktaH ko vA kalau yuge ||
The power in the holy name of Mahadeva to absolve sins is so great that it is impossible for any mortal to perform a sin greater than what can be absolved by these names.
sadA samucchareddhImAn shiva ityakSharadvayam |
samsArasAgaraM tIrtvA shivasAyujyamApnuyAt ||
By reciting two sacred letters, shi-va always, one can cross the ocean of samsAra and attain shiva sAyujya.
prasa~NgAt kautukAt lobhAt bhayAdaj~nAnato.api vA |
hara ityccharan martyaH sarvapApaiH pramuchyate ||
Whether one knows that it is fire or not, when touched, fire burns. Similarly, a person may recite the holy name of hara by chance, owing to curiosity, for accomplishing desires, out of fear or ignorance. Irrespective of all this, he shall be absolved of sins! Now, what to speak of the merits attained by reciting the name with devotion and as taught by Sadguru?
kOTayo brahmahatyAnAm agamyAgamakoTayaH |
sadyaH praLayamAyAnti mahAdeveti kIrtanAt ||
By reciting the four lettered mantra mahAdeva, one is absolved of even mahApAtakas like brahmahatyA, agamyAgamana etc.
The glory of shiva nAma is described in baDabAnala and Linga Purana as well:
vedeShu sAramakhileShu cha mantra tantra-
shAstreShu sAramapi shabdasamudrasAram |
sAreShu sAramidameva shiveti nAma
yenApi kena sakR^iduccharitaM sa dhanyaH ||
shuchitvayukto.apyashuchitvayuktaH shivaM smaran janturupaiti siddhim ||
amR^itaghaTeshwara or kAlasamhAra mUrti is an aspect of mahAdeva and can be remembered using any name of parameshwara.
1. You can recite dwyakShara mantra shiva or chaturakShara mantra mahAdeva
2. You can recite shiva sahasranAma found in mahAbhArata, various Agamas, purANas and tantras
3. You can recite hymns like shiva mahimna etc.
4. If initiated, you can recite mantras like pa~nchAkSharI, aShTAkSharI, prAsAda, prAsAda parA, mahAprAsAda, dhvani etc.
The most important aspect of nAma siddhAnta however is to never violate the code of conduct prescribed by Shruti and smR^iti:
vedo mUlaM hi dharmANAM vedamUlaM maheshwaraH |
tasmAt sarvaprayatnena vedasmR^ityuditaM param |
dharmaM shivAshrayaM prAj~naH na kadApi parityajet ||
The same is true for hari nAma smaraNa as well:
dharmasya prabhurachyutaH ||