That's understandable, it's much better to start over from the beginning that to prevent the loss of the original....Or is it?
I'm going to provide, in totally general terms, what your consultant isn't or can't, starting with.... Everything costs money. Please remember, everything is in very general terms.
1st - cost............. Lets put the day rate of an audit @ $2000 per day (we'll made it costs inclusive so it's not unrealistic)
2nd - Now all accredited Certification Bodies are required to apply a document (IAF MD-5) and it's guidance when determining audit duration (I'd almost bet your consultant doesn't know this) the audit duration requirements for Health & Safety audits are set forth in Annex C and are established by Effective Employee count and Risk............ Not knowing your circumstances or anything else I'll use a company with MEDIUM Risk @ 276-425 employees for use here. The "Total" audit duration for an initial certification (beginning to end) is set at 11 days (like I said, every accredited CB has to use the exact same chart, every single one). So now we have a starting point of 11 total audit days to get a "NEW" certificate for ISO 45001:2018 giving us a basic cost of $22,000 not counting other fees, costs, etc........... $22,000
3rd - OK moving forward, you've decided to do the MIGRATION during an annual surveillance audit, the MIGRATION rules require extra time be applied to the original audit duration (we'll use 1 day in this case). Now IAF MD-5 is again applied and it requires that annual surveillance audits be set at 1/3rd of the duration of the original "Total" duration in this case it would be 1/3rd of 11 days or 11 x 0.33 which equals 3.36 days (audit days must be in 1/2 day increments to the closest 1/2 day so now we have a 3.5 day annual audit. The 3.5 day annual audit, plus the 1 day MIGRATION comes to 4.5 days. Simple math here 4.5 days x $2,000 = $9,000
4th - Your certificate expires and once they expire OHSAS 18001 certificates vaporize, they no longer exist, they disappear and can't be extended....POOF! So now you've got to start absolutely and totally over from scratch.......... $22,000 minimum, not counting other neat fees and expenses (and they will happen) and instead of only the $9,000 MIGRATION expense you now have $9,000 + $22,000 = $31,000.... MINIMUM!
Very few consultant's that I've run into have any understanding of
IAF MD-5 DETERMINATION OF AUDIT TIME OF QUALITY, ENVIRONMENTAL, AND
OCCUPATIONAL HEALTH & SAFETY MANAGEMENT SYSTEMS; IAF MD-22 APPLICATION OF ISO/IEC 17021-1 FOR THE CERTIFICATION OF OCCUPATIONAL HEALTH AND SAFETY MANAGEMENT SYSTEMS (OH&SMS); ISO 17021 CONFORMITY ASSASSMENT - REQUIREMENTS FOR BODIES PROVIDING AUDIT AND CERTIFICATION OF MANAGEMENT SYSTEMS, or anything else related the the ACCREDITED certification process.
You can get you own copy of IAF MD-5 and MD-22 here because your consultant will probably say I don't know anything, they're free....
IAF Publications: Mandatory Documents