It is quite easy, actually. The parameter name is of the simulink block is "ExtGeomFileName"
load_model('simulinkmodel1')
% ....
% Only for Mac users
if ismac
    % Find all the blocks in the simscape model
    blocks_in_model = find_system('simulinkmodel1/system', 'LookUnderMasks','all');
    % Check for all the blocks if there exists a parameter with this filepath
    for ii = 1:length(blocks_in_model)
        try % if this param exists, replace the slash.
            filepath = get_param(blocks_in_model{ii},'ExtGeomFileName');
            macpath = strrep(filepath,'\','/');
            set_param(blocks_in_model{ii},'ExtGeomFileName',macpath);
        catch % No such param
        end %endtrycatch
    end %endfor
end %endif
Easy peazy quick-fix-squeezy

