I am trying the solution given in is-it-possible-to-change-customize-some-conversions-done-by-texform which works very well except changing the order of the Format command causes an error on some symbols.
I do not know if this is Mathematica own issue with the command Format or if it is related to the package I am using.
First I installed the nice package MathematicaTeXUtilities using the command
Get["https://raw.githubusercontent.com/jkuczm/MathematicaTeXUtilities/master/BootstrapInstall.m"] Here is MWE. Using the following order, with fresh kernel, show no error
Needs["TeXUtilities`"] Unprotect[Hypergeometric1F1,HypergeometricU]; Format[ Hypergeometric1F1, TeXForm] = TeXVerbatim@"\\operatorname{Hypergeometric1F1}"; Format[ HypergeometricU, TeXForm] = TeXVerbatim@"\\operatorname{HypergeometricU}"; Protect[Hypergeometric1F1,HypergeometricU]; Now, changed the order of Format command, and using fresh kernel (must restart the kernel to see the error), an error message shows up
Needs["TeXUtilities`"] Unprotect[Hypergeometric1F1,HypergeometricU]; Format[ HypergeometricU, TeXForm] = TeXVerbatim@"\\operatorname{HypergeometricU}"; Format[ Hypergeometric1F1, TeXForm] = TeXVerbatim@"\\operatorname{Hypergeometric1F1}"; Protect[Hypergeometric1F1,HypergeometricU]; 
I thought at first that the order of symbols in Protect has to match the order of Format commands. But this does not make sense. And I found by trial and error a case where the errors show up even when the order or Protect match order of Format. Here it is (fresh kernel)
Needs["TeXUtilities`"] Unprotect[HypergeometricU,LaguerreL,HermiteH,Hypergeometric1F1,Erf,Erfc]; Format[ HypergeometricU, TeXForm] = TeXVerbatim@"\\operatorname{HypergeometricU}" Format[ LaguerreL, TeXForm] = TeXVerbatim@"\\operatorname{LaguerreL}" Format[ HermiteH, TeXForm] = TeXVerbatim@"\\operatorname{HermiteH}" Format[ Hypergeometric1F1, TeXForm] = TeXVerbatim@"\\operatorname{Hypergeometric1F1}" Format[ Erfc, TeXForm] = TeXVerbatim@"\\operatorname{Erfc}" Format[ Erf, TeXForm] = TeXVerbatim@"\\operatorname{Erf}" Protect[HypergeometricU,LaguerreL,HermiteH,Hypergeometric1F1,Erf,Erfc]; 
So I am not sure what is going on now. Any ideas?
As a workaround, now I Format them one by one, instead of the batch mode and error went away
Needs["TeXUtilities`"] Unprotect[Hypergeometric1F1]; Format[ Hypergeometric1F1, TeXForm] = TeXVerbatim@"\\operatorname{Hypergeometric1F1}"; Protect[Hypergeometric1F1]; Unprotect[HypergeometricU]; Format[ HypergeometricU, TeXForm] = TeXVerbatim@"\\operatorname{HypergeometricU}"; Protect[HypergeometricU];