yes, they'd freeze your pension. I find it ironic that there are some expats that have a problem with guys that can support themselves, but do not have the financial requirements to obtain an 'O' visa extension, but maybe some of the guys that ridicule them are getting the annual pension increase on the fiddle.
2.5% on 800k gives you 20k THB a year, that'll nearly pay for an agent to do your visa, saving you all the headache of doing it yourself. Waiting now with bated breath for all the replies from the righteous expats who seem to have a problem with guys using an agent.
If your from the UK., the DWP., which is the government dept., that pays your pension, if you give them details of a foreign bank they'll pay your pension into that account. You don't need to transfer it from a bank in the UK.
Here's one for you. You say retirees who stay in Thailand over 180 days have income from overseas, like pensions they haven't paid tax on have to pay tax in Thailand. So what if you only receive a state pension (UK), that is below the tax threshold in the UK, therefore not taxable, in this scenario what would be any taxation in Thailand?