Is there a consistent rule to create reflexive verbs?
When utilizing reflexive verbs are all verbs able to become reflexive verbs by adding,
se at the end of the infinitive verb?
"lavarse", "tomarse", "rascarse"
Yes, and it's the rule you wrote yourself, adding se to the infinitive.
As all infinitives end in -ar, -er or -ir, adding se is totally regular and consistent.
At least grammatically, because there may be some verbs that are semantically unable to become reflexive, I.E. it wouldn't make any sense that the subject and the object be the same, although I'm not sure and can't name any right now.
As @Eduardo suggests, the verbs nacer and parir can't by logic be reflexive.
Another examples are llover, haber (when not acting as an auxiliary verb*) this two verbs don't have a subject (nobody rains) so they can't be reflexive.
* haber means there is in this case. When acting as an auxiliary as in haber ido (have gone) can be reflexive, but that's a different case.